Conceptualising party-driven movements

This article contributes to scholarship on the relationship between political parties and social movements by proposing the concept of ‘party-driven movements’ to understand the formation of a new hybrid model within existing political parties in majoritarian systems. In our two case studies – Momentum’s relationship with the UK Labour Party and the Bernie Sanders-inspired ‘Our Revolution’ with the US Democratic Party – we highlight the conditions under which they emerge and their key characteristics. We analyse how party-driven movements express an ambivalence in terms of strategy (working inside and outside the party), political aims (aiming to transform the party and society) and organisation (in the desire to maintain autonomy while participating within party structures). Our analysis suggests that such party-driven movements provide a potential answer to political parties’ alienation from civil society and may thus be a more enduring feature of Anglo-American majoritarian party systems than the current literature suggests.


Introduction
An important body of literature seeks to bridge the divide between the study of political parties and social movements, examining the interface between the two (Kitschelt, 1993;Kruszewska, 2016;McAdam and Tarrow, 2010;Schwartz, 2010). Recently, Donatella Della Porta et al. (2017) have analysed new 'movement-parties', hybrids which have emerged from left-wing, anti-austerity movements and shaken up the party system in Greece, Italy and Spain. The prospect of a similar development in majoritarian, two-party-dominated systems like the United Kingdom and the United States, is far less likely. Indeed historically, a more fruitful strategy for movements in these systems has been to form mutually beneficial relationships with existing party organisations (Schlozman, 2015).
In this article, we argue that the differing dynamics of two-party systems has resulted in the appearance within existing parties of an alternative form of hybrid organisation, which we call 'party-driven movements'. We aim to provide a conceptual framework for understanding the emergence of this new organisational hybrid. Two questions guide our research: first, under what specific conditions do party-driven movements emerge? Second, what are their key features and to what extent are they a distinctive kind of organisation?
On this basis, we aim to advance the literature along two lines. First, rather than social movements that have evolved into parties, our two case studies represent movements that have emerged from the party itself: initiated by internal actors who co-opt existing networks of movement actors to create a movement-wing. Thus, rather than movements adopting more formal organisational structures and methods of political contestation, we seek to explain how, in this process, parties have adopted certain aspects of movement organising, while at the same time maintaining many of the traditional structures and functions of political parties that underpin success in parliamentary politics.
Second, we turn attention from continental European multi-party systems to Anglo-American two-party systems. We claim that there are specific factors in the emergence of party-driven movements that are more evident in two-party systems. They may, furthermore, represent an attempt by party actors to reforge the links with civil society undone by professionalisation and centralisation (Mair, 2013), and which have inspired attempts to restructure them (Yishai, 2001), or to explore alternative representative vehicles (Dommett and Rye, 2018).
Sometimes this process is initiated by party leaders, such as Obama's community organising initiative, 'Organising for America', and Labour's past experiments with similar techniques (Geary and Pabst, 2015). In contrast, our two case studies concern movements that emerged in opposition to mainstream party leaders, articulating dissatisfaction with the failure of party elites to adequately represent members' interests and political goals. At the same time, they appeal beyond current members to disillusioned former members and participants in social movements who have never been members before.
In each case, a window of political opportunity was opened by a sudden upsurge of energy in support of a candidate and a policy agenda. Forming a movement was a means by which actors, within the party, could harness it to serve longer-term left-wing goals, drawing in new support from new, non-traditional sources. This party-movement dynamic, we argue, is the basis of a potentially transformative relationship, producing a new kind of organisation.
We argue that this latest evolution in political party organisation is one avenue through which political parties could seek to reconnect with civil society. While at this stage it is not clear the extent to which this hybrid model could spread to other political systems, our analysis suggests that its most fertile ground appears to be in majoritarian two-party systems. The successes of Momentum and Our Revolution as organisations capable of mobilising supporters shows clear potential, although these movements have not yet demonstrated clear payoffs with national electoral victories.

Structure of the article
After exploring existing literature on the topic, we proceed by examining four key conditions for the emergence of party-driven movements, (1) unrepresented claims, (2) preexisting social movement networks, (3) political opportunity structures, and (4) leadership. We then identify from our case studies four shared characteristics which illuminate the distinctiveness of the party-driven movement: (1) insider/outsider status, (2) the nature of its agenda, (3) independence/autonomy, and (4) digital organising.
The material we analyse comes largely from Our Revolution and Momentum themselves, including publicity material, web-pages, newsletters and general information available online and offline, similar to an 'official story' approach to gathering data on political organisations (Poguntke et al., 2016). This has been supplemented with material from external sources, such as news publications as well as existing scholarship on the two organisations.

Social movements and political parties
Scholars interested in political parties have tended to view social movements as peripheral to their core concerns (Della Porta, 2015) and vice versa (Goldstone, 2003). Social movements are seen as 'challengers' looking to gain access to institutionalised politics (Tilly, 1978), and even as parasitical upon the party system (Schattschneider, 1948). More recently, however, some scholars have sought to emphasise the mutual dependencies and overlaps between parties and interest groups or movements (Goldstone, 2003). As 'political organisations', for example, they are both a form of political 'linkage' and should be considered as part of a common research agenda (Fraussen and Halpin, 2018).
Strong relationships between parties and social movements are a long-standing feature of political organisation. Parties are gatekeepers to power and potential agents of change. They are therefore always likely to be potential targets for groups, organisations and movements that seek political change (Allern and Bale, 2012: 8). The particular form that these relationships take can vary: movements may create new parties (Della Porta et al., 2017), they may integrate with existing ones, or form looser, but close, associations. The strategy pursued depends, in part, on the particular dynamics of the party system concerned, as Cowell-Meyers (2014) has argued.
For example, social movements may, first, create or initiate parties. This may be strategic (to pursue power) or tactical (to achieve a specific campaigning goal). The Labour Party, which emerged in the twentieth century from trade unions' efforts to promote and strengthen working class representation (in alliance with socialist and reformist societies), benefitted from the expansion of the franchise and the collapse of the Liberal Party. More recently, left-libertarian and Green movements (Kitschelt, 1988(Kitschelt, , 1989 have emerged onto the formal political landscape, and in some cases, such as the German Greens, have become governing parties. These parties, while initially reflecting the social movement organisation from which they emerged, are likely, eventually, to become more formally routinised and institutionalised (Koopmans, 2004;Offe, 1990;Tarrow, 1994;Van Biezen, 2005), albeit retaining some of their previous identity (Kitschelt, 2006). Similar assumptions underlie della Porta and colleagues' analysis of a more recent wave of hybrid 'movement parties' in Europe, emerging in the wake of the 2008 financial crash. Drawing on three case studies -SYRIZA in Greece, Podemos in Spain, and Italy's 'Five Star Movement' (M5S) -they conceptualise them as transitional organisations, beginning as anti-austerity and anti-establishment mobilisations, characterised by 'shallow, weak, and opportunistic organization' (Della Porta et al., 2017: 15) and destined to become formalised political parties.
New parties may also be formed as a campaigning tactic by social movements to influence more established parties. Cowell-Meyers (2014) argues that the Northern Ireland Women's Coalition (NIWC) had a successful impact on patterns of representation in the province in this way. In a proportional electoral system, they were able to gain enough of a voice to influence the political process and initiate a dynamic of 'contagion' (Duverger, 1963), in which more dominant parties began to compete to adopt its agenda to improve the representation and participation of women in Northern Ireland politics.
However, the dynamics of two-party majoritarian systems (Ware, 2009) create significant barriers to the entry of new parties, meaning other strategies may be more promising and plausible. Thus, in these circumstances, it may make more sense for social movements to enter into integrated relationships with already existing political parties. There are broadly two different strategies by which such a state of affairs may come about. A party may deliberately cultivate relations of co-ordination with a movement (even eventually co-opting it wholesale), or a social movement may enter into a party as part of an invasive or hostile strategy (Schwartz, 2010), creating a movementwing within the party.
In the first of these scenarios, outlined comprehensively in the US context by Schlozman (2015), cooperation may be an especially attractive move in systems where 'traditional political organisations have receded' and the parties have been 'hollowed out' (Schlozman, 2015: 22) becoming 'more permeable and more dependent on outside groups' (Schlozman, 2015: 27). Parties and movements form these kinds of relationships because there are mutual benefits. Key to this, he argues, is that internal elite gatekeepers see a path to victory and durable electoral majorities resulting from the arrangement. In an era of declining party membership rates (Van Biezen et al., 2012), social movements could be seen as a source of revitalisation and renewal for political parties.
However, Schlozman's model focuses on a specific type of voluntary 'anchoring' relationship between parties and movements. He -quite explicitly -does not concern himself with hostile or aggressive strategies. But existing party leaders may not always have the decisive say as to what groups become involved in their organisation. Protest movements or other activist organisations may form new factions within the party or take over existing ones with the aim of attempting to take control of it. Schwartz (2006Schwartz ( , 2010 focuses more specifically on this kind of relationship, in which movements begin outside of parties and work their way in. As well as the kind of collaborative approach outlined above, movements may adopt invasive strategies (involving 'insurgency' on behalf of an alternative ideology or leader, takeover or co-optation), or hostile strategies (including disruption, discrediting opponents, purging). The Tea Party's relationship with the US Republican Party could be characterised in this way (Williamson et al., 2011).
Third, social movements and political parties may associate closely, forming loose, overlapping connections to each other's mutual benefit without seeking to integrate. Several mechanisms might link movements and 'routine political actors', including the adoption of strategies, collective action repertoires and forms of movement organising (Kruszewska, 2016;McAdam and Tarrow, 2010;Szabo, 2015) by parties or by movements joining electoral coalitions or engaging in electoral mobilisation (McAdam and Tarrow, 2010: 533). These relationships may take the form of 'exchange relationships': groups for instance may provide expertise in key policy areas, as well as information, resources and support which makes cooperation attractive to parties (Allern and Bale, 2012). An initial incentive for interaction is the imperative of organisational survival and is more likely where there is a 'certain degree of overlap . . . between the party and the social movements' identities' (Piccio, 2012: 268). What may emerge from this is a beneficial form of mutualism that arises from the fact that each has control over resources the other needs (Witko, 2009: 221), reinforced by the political environment, institutions and structures (Witko, 2009: 227). This, in turn, fosters overlaps between party and movement personnel and the reinforcement of shared networks. Banaszak (2010) has highlighted (in the context of state-movement relations) the importance of the physical presence of activists both inside the institution (i.e. the party in this case) and outside (in wider movement networks), providing a basis on which the movement and party organisations can begin to work together.
We build on and add to this literature, arguing that there is an emergent new dimension to the party-movement relationship in the form of the party-driven movement that has emerged within parties, while maintaining a distinctiveness from them. These movements differ from Della Porta et al'.s transitional 'movement parties', from Schlozman's 'anchoring relationships', the hostile 'invaders' of Schwartz and from McAdam and Tarrow's electoral coalitions. Nor are they quite adequately described, in our view, as 'movement factions' which resemble party-affiliated factions (Dennis, 2019). They are characterised by integration on the one hand, and distinctiveness on the other. These, we argue, represent a variation in the relationship between movement and party which may have a longer-term impact on the evolution of the latter and which therefore requires its own explanation. In the next section, then, we introduce our two main case studies before going on to conceptualise party-driven movements.

Momentum
Momentum was the brainchild of Jon Lansman, a long-standing left-wing Labour activist who had worked on Tony Benn's deputy leadership campaign in 1981. Along with Adam Klug, Emma Rees and James Schneider as national co-ordinators, he launched the organisation in 2015 following Jeremy Corbyn's victory in the party's leadership ballot as a means of harnessing the political energy generated by his campaign. A key purpose of this new organisation was to build support for Corbyn's policy agenda and a left-wing agenda more generally (Wintour, 2015a). By 2018, Momentum reported that it had reached 40,000 members, with 15 members of staff, 170 local groups and over 95% of its funding coming from membership fees and small donations (Cowburn, 2018).

Our revolution
Our Revolution was founded in August 2016, a successor to the Bernie Sanders campaign for the Democratic presidential nomination and an attempt to continue to promote the campaign's agenda. It was established as a social welfare organisation (known as a '501(c)(4)') with its key objective to 'transform American politics to make our political and economic systems once again responsive to the needs of working families' (Gautney, 2017). The organisation's staff and board of directors came largely from campaign organisers and volunteers. Key figures include Nina Turner (President), a politician from Ohio who initially backed Clinton and then switched to Sanders in 2015, becoming 'one of the most prominent black voices to stump for Sanders' (Meyerson, 2017), and Larry Cohen (Chair), former President of Communication Workers of America who worked on his campaign as a liaison to organised labour.
We employ these case studies as illustrative examples for a plausibility probe of our theory on the emergence of this type of hybrid organisation. We believe that these two case studies help to illustrate and add substance to the theoretical framework we set out in this article. This framework provides a foundation for more empirical testing.

Conditions of emergence
In the following analysis, we argue that four common elements shape the conditions under which these party-driven movements emerge: (1) issues -that there are unarticulated or unrepresented claims that seek expression in the political system; (2) peoplethat there is a critical mass of potential supporters in pre-existing movements and organisations who can be galvanised behind those claims; (3) access -that opportunities exist to articulate and galvanise support behind those claims; and (4) leadership -that there is a figure, and a campaign, around which different organisations, campaigns and actors can coalesce into a single movement. This structure draws from key ideas in political process theory-political opportunities, mobilising structures and framing processes -for understanding the emergence of social movements while seeking to highlight what is unique and distinctive about the particular situation of movements arising from within political parties in the context of two-party majoritarian systems.

Issues: Unrepresented claims
Kitschelt has argued that new parties are likely to emerge 'only where an intensively felt, salient political interest harbored by a quantitatively significant constituency lacks representation in the existing party system' (Kitschelt, 2006: 282). The domination in recent years of centre-left parties by 'centrist' leadership groups has meant that in the wake of the 2008 Global Financial Crisis, more radical voices on the anti-austerity left have struggled to be heard in mainstream political debate, despite significant support. This opens a gap for alternatives to the mainstream parties. In Spain, for example, this was one of the factors behind the rise of Podemos (Ramiro and Gomez, 2016). However, as we have suggested, in majoritarian systems like the United States and the United Kingdom, thresholds are high for the establishment of new parties. Therefore -where other conditions are satisfied (especially a relative organisational openness) -these unrepresented claims can form the basis of an appeal by radical campaigns and movements within the existing party system.
In the United Kingdom, Corbyn supporters have been found by Paul Whiteley and colleagues to have been disenchanted with politics-as-usual and yearning for a new style of politics not represented by the former Labour leadership (Whiteley et al., 2019). Labour failed clearly to articulate an anti-austerity position, and consequently faced a challenge from a new coalition of internal and external left-wing forces united by an antiausterity outlook. In the leadership contest that followed electoral defeat in 2015, Jeremy Corbyn articulated the frustration of many members and voters about the impact of government spending cuts conducted in the name of 'austerity' (Klug and Rees, 2018). Specific policies not being articulated by the Labour leadership at the time included renationalizing Britain's railways, giving up its nuclear weapons, replacing the House of Lords with an elected chamber, cracking down on tax evasion and strengthening the power of trade unions. Tapping into pre-existing voter concerns, in combination with the right candidate, provides an ideological core around which a coherent, sustainable movement can emerge from within existing party structures.
Supporters of Our Revolution in the United States have mobilised around a wide range of issues. A survey of the dozens of affiliated local groups (Our Revolution, 2019) indicates that while they tend to have a localised rather than national focus in their stated aims and objectives, they have coalesced around a number of significant common issues which underpin a national appeal and resonate with the Sanders policy platform. These include campaigning for the right to universal healthcare coverage, against global warming, for greater economic and social equality and against the excessive power of 'corporate America' (see, for example, Cuyahoga County Progressive Caucus, 2019; Our Revolution, 2019a; Progressive Democrats of America, 2019; Sacramento Progressive Alliance, 2019). The stated ambitions of these groups are to 'spend our money on education and job creation rather than incarceration . . . (and) see that people have access to affordable health care from before birth to last breaths' (Our Revolution, 2019b), to 'raise awareness, educate, and mobilize our local communities in the fight against inequality in all its forms' (Our Revolution, 2019c) and to reclaim 'our government from the special interests and corporations that have overshadowed the voice of the people' (Our Revolution, 2019d).

People: Pre-existing social movement networks
For unrepresented claims and interests to enter into an existing political party, there needs to be some form of pre-existing organisation and network that is capable of doing so. Preexisting movements, organisations and campaigns are a significant resource on which party organisations draw and, under the right conditions, will form the basis of new movement-party hybrids. Thus, there needs to be a large enough base of movement supporters willing to join the party. In centre-left parties in particular, left-wing factions appear most likely to form party-driven movements because of members' traditionally strong links and familiarity with progressive social movements (Kriesi, 2015;Kriesi et al., 1995;Della Porta, 1996). Key to this is the overlap between activists both inside and outside the party (Banaszak, 2010) form networks that cut across the party's boundaries. Both Momentum and Our Revolution have benefitted from the activation and galvanisation of these networks.
A significant contributor to Corbyn's success was its appeal to anti-war, anti-austerity and anti-racism campaigners, students, and traditionally 'outsider' groups on the left which helped form the basis of Momentum (Earle, 2018;Klug and Rees, 2018), along with a range of Labour and former Labour members. As Jon Lansman explained: You had the pre-existing Labour left, which was tiny, of course. But they had influences. Then you had a left that was outside of the Labour Party but was part of the traditional left. Stop the War was part of that. Then there were lots and lots of returners who had left at all sorts of times. People who had left in the 80s and the 90s and over the Iraq war were coming back. Then you had these people who were completely new to the Labour Party. Most of them had not been in other left parties, or if they had it was the Greens, and the social movements . . . (Ghadiali, 2018) Whiteley and colleagues observe that of the post-2015 recruits to the Labour Party, those who rejoined after their membership had lapsed tended to be more left-wing than current members, indicating that sections of the far left had rejoined the party (Whiteley et al., 2019).
It is clear from the number of different groups working directly under the Our Revolution banner how this has acted as a rallying point for groups that had hitherto been outsiders. Long-standing radical and fringe campaigning groups like the Democratic Socialists of America, Progressive Democrats of America as well as a cornucopia of state and local organisations have cohered under the banner of Our Revolution, motivated by the core common concerns outlined above. Democratic Socialists are 'inspired by Bernie's call for a political revolution' (Our Revolution, 2019e). Campaigns like the Democracy Project in Los Angeles see participation in Our Revolution as part of their mission to 'unite Democrats, Green Party, Democratic Socialists and Independents behind liberal causes, legislation and candidates' (Our Revolution, 2019f). Other groups are 'bringing together a coalition of (local) progressives . . . from all the various communities who support progressive change' (Our Revolution, 2019g) and seeking to 'act as an intermediary between groups, uniting specialty organizations . . . into a more cohesive movement' (Our Revolution, 2019h). In California, for example, 'local grassroots volunteers, activists, and leaders' have come together under the Our Revolution banner 'to fight for issues and values that are critical in our community' (Our Revolution, 2019i).

Access: Political opportunity structures
The high thresholds for new parties in two-party majoritarian systems means success for Our Revolution and Momentum was more likely to come by exploiting opportunities to influence and transform dominant parties from within. In the United States, weak party organisation provided this opportunity. The Democratic Party, for instance, is characterised by some as merely a series of 'state-run ballot lines' over which leaders have no control (Schulman, 2016: 2). This means that radical political organisations such as the Democratic Socialists of America are likely to have a greater electoral impact by fielding or supporting candidates within the Democratic Party's primary system (Democratic Socialists of America, 2019), than by running as an independent party. There is a long history of this potentially fruitful strategy (Schlozman, 2015) and the same kind of calculation was significant in Bernie Sanders' decision to run for the Democratic nomination rather than as an independent Presidential candidate (Nader, 2016).
In the UK's parliamentary system, however, such a move by a party outsider would be impossible. According to party rules, Labour's leader (and thus candidate for Prime Minister) must be 'elected or re-elected from among Commons members of the PLP [Parliamentary Labour Party]' (Labour Party, 2018a: 4). However, Corbyn's leadership bid was facilitated by the relative openness of the party's new leadership election procedure, established in 2014. It gave the franchise to a new category of 'Registered Supporters' -non-members declaring support for party values and paying a small administration fee, set at £3 (Wintour, 2015b). Although nowhere near as open as a Democratic primary, this was nonetheless a major factor encouraging the flowering of a new movement around Corbyn's non-mainstream candidacy because it enabled many thousands of non-members to sign up specifically in order to vote for him. 1 Jeremy Corbyn won with a landslide victory on 12 September 2015 with 59.5% of the vote (215,417).
In both these cases, party election rules created an opportunity to draw in support from beyond the existing party boundaries. This supports and extends the physical presence of activists both inside and outside the party boundaries which is necessary to address the claims of these new movements. One final factor, however, is necessary to draw all of this together: a leader.

Leadership
Crucial in each case was a unifying figure -Corbyn and Sanders, respectively -around which these movements could coalesce. Neither were conventional leadership figures (both were considered 'outsiders'), but they were the right kind of leader in the circumstances, representing an opportunity for a change of direction and an anti-elitist appeal.
Corbyn was the most rebellious of Labour backbenchers over many years and was consistently at odds with the party leadership on a variety of issues (Cowley, 2005: 49-53), while Sanders had made a career out of not being a Democrat (despite caucusing with them in the Senate). This assisted with the appeal of both candidates to non-party activists on the left and succeeded in attracting many of them into their respective parties. Corbyn, for instance, was perhaps uniquely able to bring together anti-austerity, anti-war, Labour, non-Labour and ex-Labour leftists in addition to new waves of enthusiasts (Ghadiali, 2018). Combined with the opening-up of Labour's leadership election, this enabled thousands of new members and supporters to support his campaign (Poletti et al., 2016). Out of this movement, Momentum was born.
Many Our Revolution groups are explicit about the fact that they are 'a spin-off of the Bernie Sanders campaign' (Our Revolution, 2019j), 'inspired by Bernie Sanders' (Our Revolution, 2019k), and 'dedicated to the continuation of the revolution that Bernie Sanders ignited in us' (NYPAN, Southern Finger Lakes, 2019). As such they are 'inspired by Bernie Sanders' vision' (Our Revolution, 2019) and 'abide by (his) . . . principles' (Our Revolution, 2019l).
While clearly anti-elitist in tone, does this amount to a populist appeal? It was certainly popular, particularly in Corbyn's case, and both individuals were in some sense important embodiments of the movements that have respectively coalesced around them. One difficulty is that 'populism' is a sometimes vague and often misused term. Cas Mudde, usefully defines it as: a thin-centred ideology that considers society to be ultimately separated into two homogenous and antagonistic groups, 'the pure people' versus 'the corrupt elite', and which argues that politics should be an expression of the volonté générale (general will) of the people. (Mudde, 2004 cited in Mudde andKaltwasser, 2013: 149-50) While there may have been some element of this in their appeal, it would be difficult to argue that either Corbyn's or Sanders' platforms were based solely on such a naked appeal to unbridled 'populism'. In both cases, their political ideologies could be described as a more fully developed form of social democracy (or democratic socialism as Corbyn describes himself) rather than the more 'thin' and malleable form of populism. On the other hand, if we switch attention to the specific intra-party appeal, this may yield slightly different answers. Watts and Bale (2019) have argued that Corbyn's appeal amounted to a kind of 'intra-party populism' serving as a 'corrective' to a party democracy that had stopped serving its members, and appealing to their wisdom against a corrupt and misguided elite. One of Corbyn's objectives was to reform internal party democracy to make Labour more of a member-led organisation.
While this may be open to debate, more important arguably is that both Sanders' and Corbyn's campaigns, could be characterised in Schwartz's (2010) terminology by coordinated interaction between internal party actors and external movements. More important than an appeal to existing party members alone, was a capacity to draw new people in (as discussed above). However, this is qualified by the fact that existing senior leadership figures did not play a significant role. Indeed, their attitude was at different times complacent, indifferent, hostile and bewildered. The co-ordination that was taking place in these cases was (initially) between apparently marginal actors: the radical fringes of the party and left-wing groups outside its formal boundaries. In this respect, then, their campaigns additionally demonstrated some characteristics of insurgency, and even hostile takeover, which perhaps adds some credence to the intra-party populism argument. Whether we would call it populist or not, leadership of these movements came from marginal figures whose reputation and appeal was based on their status as long-standing outsiders running against the existing hierarchy.

Key characteristics
Party-driven movements can be identified by four key characteristics. Three reflect a kind of ambivalent 'Janus' strategy which seeks to engage with and influence, if not control, the direction of the party by getting into positions which make it possible to marshal its considerable resources in favour of its preferred priorities. At the same time, the party benefits from the resources the movement brings, especially committed, engaged activists. This reflects the fourth characteristic, a specific movement-style of organising which is mostly digitally based, and which acts independently of the party itself, while being closely aligned with it.

Insider/outsider status
A traditional characteristic of formal organisations like mainstream parties is clearly maintained 'formal' boundaries -for example, by means of a membership scheme -as well as 'informal' ones marked out by shared language and practice (Rye, 2015: 303-304). Party-driven movements do not conform to such clear demarcations. They are characterised by an ambivalent relationship with the party itself, operating within it while seeking to maintain an 'outsider' status (Selfa, 2008).
This, in part, reflects the ambiguities of their origins in networks operating across the party's internal and external fringes. But it also reflects a suspicion of mainstream partypolitics and demonstrates the potential for a clash of organisational cultures. Party-driven movements adopt from social movements a more horizontal structure which contrasts with traditional, often hierarchical or (in Labour's case) federal forms of party organisation adding to the semi-detached relationship between the two. At the same time, there are good, strategic reasons for this 'Janus' strategy that recognise the limits of extra-parliamentary action. Momentum founding national organisers, Adam Klug and Emma Rees (2018), for instance, advise progressives to 'take the movement into the party' because it is likely to be a more effective strategy. They point out that even the most heavily supported protest can be ineffective on its own: for example, the anti-Iraq War protests in February 2003 (which organisers estimated 1.5 million attended) failed to stop the UK's involvement in the war (Klug and Rees, 2018). They argue instead for an 'insider-outsider strategy, linking movements and the party to create a movementparty' (Klug and Rees, 2018). The aim is to connect vibrant movements with an organisational structure capable of influencing political decision-making at a governmental level. They argue for the strong benefits of a strategy which maintains a significant level of autonomy from the party in an independent organisation, since it enables the movement to act as an independent voice within it. Some might argue that this is an attempt by movements to have it both ways, riding on an anti-politics wave as 'outsiders' but for relatively conventional political purposes (Dennis, 2019: 7). However, it also reflects a wider ambivalence on the left towards electoral politics. The attempt to straddle both worlds in the case of Our Revolution is a response to the 'classic dilemma' of American radical politics: whether to struggle within the Democratic Party or create an alternative to it (Uetricht, 2017: 26). Sanders has sought to strike a balance between these strategies: his detachment from the Democratic Party means he has not been subject to the same compromises as other potential candidates, even as he has worked and caucused with Democrats in the Senate for many years.
For many radicals, the Sanders campaign was a vehicle for the outsider left to 'be in the room' (Lenchner, 2015: 64). It provided 'an opening for grassroots energy' and exploited a 'vibrant and open membrane between anti-capitalism and Democratic politics' (Lenchner, 2015: 65). Even among his critics on the left, there is a recognition that Sanders 'would not have reached this vast audience if he hadn't run in the Democratic primary' (Serge, 2016). Our Revolution is a product of this approach -it is both seeking to change the Democratic Party from within and agitate from without (Uetricht, 2017). Even after the defeat of Sanders' presidential nomination in 2016, activists continued to mobilise through Our Revolution due to the popularity and perceived success of this form of organising. Although they lost the nomination, Sanders performed much better than expected and activists saw this as the beginning rather than the end of their campaign. This was an opportunity for a range of oppressed and marginalised social groups to articulate their grievances through a transformative programme without losing their group specificity (Young, 1990).
There is a mutual benefit to party and movement cooperation. The movement provides the party with fresh energy and new members, while the party provides the structure for the movement to make further political advances. However, there is an ever-present danger in such strategies of co-option or absorption (Schlozman, 2015), and for many on the radical left in the United States, collaboration with it is at best a temporary measure, providing a platform for an independent left wing party (Finger, 2015;Meyer, 2016;Schulman, 2015), and at worst a betrayal, binding activists to a neo-liberal party (Smith and Selfa, 2016). With this in mind, the Our Revolution Group in Casper, Wyoming warns that its existence 'represents the seeds of that potential third party and also presents a cautionary tale to the Democratic Party of the critical importance of returning to its New Deal populist, progressive roots' (Our Revolution, 2019m), which suggests that the longer-term maintenance of this coalition is highly contingent.

Agenda: Reforming the party and transforming society
Ostensibly, this ambivalent 'Janus' strategy is manifested further in an apparent tension between two types of goal: reforming the party on the one hand and transforming society on the other. In the former case, party-driven movements seek to strengthen support for particular policy platforms or ideological positions within the party. They may act as internal pressure groups, pushing for policy change, for example, to expand government investment in public services, state supported health care and higher education, redistribution of wealth or the public control of key services or industries, as both Momentum and Our Revolution do (Momentum, 2018;Sanders, 2016). This reflects the priorities of new movement-inspired members who tend to be more politically radical than mainstream party members (Poletti et al., 2016).
However, seeking to reform internal party bodies for instance, while an inward-facing activity, does not necessarily contradict or undermine these activities. Indeed, such a strategy is rooted in the recognition that significant social change is only possible with a radical government supported and patrolled by a powerful social base of mobilised citizens. From this point-of-view, the process of transforming parties and their personnel is an important first step to achieving more ambitious political goals. These movements need to struggle over resources available within the party in order to gain more power to implement their programmes. In short, if the party is to be a tool for transforming society it is crucial to first transform the party.
In 2017, Labour launched a 'Democracy Review' with the aim of altering its structure and rules to make it 'a more open, democratic, member-led party that's ready to win elections' (British Labour Party, 2018a; Momentum, 2018), including a membership system 'opened up to include supporters of other movements' (Momentum, 2018). This was based on the observation that making the party more internally democratic and broadly based would end Labour's 'severance from a significant chunk of its social base' and enable it to reconnect to the electorate (Savage, 2016). Democratic reform and greater openness, it was hoped, would encourage mass participation and enable the mobilisation needed to build political power and win elections. Such reforms are often contentious, and many of the key proposals for party reform were put on hold for a year at the party's 2018 National Conference (Stewart and Elgot, 2018).
Similarly, Our Revolution -as part of its Transform the Party agenda -is 'attempting to effect a transformation of the party' through a 'major realignment' towards a 'more pro-worker agenda' (Uetricht, 2017: 21-22). This requires a fundamental change in the party structure and rules as Larry Cohen (Chair of Our Revolution Board of Directors) has argued: 'a key part of the work of changing Democrats for the better involves changing the governance of the party itself' and building 'a network of decentralised, placebased political organisations' in its place (Aranoff, 2018: 3). 'Big organising' techniques have been adopted to build a grassroots campaign which relies on small donor fundraising rather than big corporate donations (Bond and Exley, 2016).
A potential barrier to this strategy is the organisational traditions and strength of the party concerned. Democratic Party organisation is notably weak, as discussed, which leaves it relatively open to well-organised movements and thus to change. However, Labour's organisation is much stronger and traditionally based on the representation of key internal constituencies of interest, including trade unions, constituency parties and elected representatives. The relatively horizontal, direct democratic nature of social movement organisation is a significant challenge to these traditions and such moves inevitably come up against resistance from forces in the party, including trade unions, who wish to protect them. This may, as in Labour's case, reflect historical experience of hostile entryism by outside groups (see Shaw, 1988), which makes change more complex.
Another element of its strategy is to get sympathetic candidates elected to office. As part of the organising efforts of Our Revolution, 46 democratic socialist candidates won primaries in 2018 (Democratic Socialists of America, 2018). Their campaign succeeded in shifting perceptions about 'socialism' especially among younger voters. Thus, Our Revolution 'engages in local party building and running progressive candidates' (Gautney, 2017), for everything from seats on education boards and state senates to gubernatorial and mayoral races. This is a significant strategy of many local groups (e.g. Our Revolution New Mexico, 2019; Our Revolution Northern Virginia, 2019; Our Revolution Oklahoma, 2019).
One important tactic for Our Revolution has been taking over party organisations at the state level. In California, for example, activists have attempted to 'aggressively push one of the country's most progressive states into playing a vanguard role' (Uetricht, 2017: 25) through organising and mobilising in internal party elections (normally unremarkable, low-profile affairs). These forms of organising have also occurred in Washington State, Hawaii, Nebraska, and Florida where mobilised local groups and campaigning organisations have challenged mainstream Democrats.

Independence/autonomy
The relationship between the political party and a party-driven movement is an unusual one. While the latter seeks to change the former from within, as we have outlined, it also tries to maintain autonomy from it. This distinguishes it very clearly from a mere faction. Rather than organising within the party as a sub-unit, party-driven movements exist as distinct, legally constituted organisations in their own right. As such, they are vulnerable to accusations of 'entryism'. Momentum, for instance, have been accused it of being a 'party within a party', aiming at a hostile take-over.
These concerns are not surprising given Labour's history and the movement's positioning of itself on the boundary between the Labour Party and a non-Labour left, historically sceptical of the party itself, but attracted by Corbyn's agenda and galvanised by his campaign. The Registered Supporters scheme, as outlined above, made it straightforward for such individuals to participate in the leadership contest. Since then, Momentum has reformed its membership rules in an attempt to get around entryism fears. Since January 2017, Momentum members must also be party members (Cowburn, 2017;Momentum, 2017a), which has arguably eroded its independence.
What remains key to Momentum's independence is that the organisation retains its own organising structures and (notably complex) ownership arrangements (Ball and Le Conte, 2016). Momentum's independent decision-making capacity is formally governed by a National Coordinating Group 'which includes representatives of members, affiliates and Labour public office holders, as well as being elected ordinary members through a digital democracy process' (Momentum, 2017a), but it has some unusual features for an apparently member-led organisation: Momentum may look and act like a grassroots organisation . . . it's actually that most capitalist of things, a private company, the successor to 'Jeremy Corbyn Campaign 2015 (Supporters) Limited' . . . with one director, Jon Lansman. (Cadwalladr, 2016) Such an organisational structure has allowed Momentum to hold on to its own contact lists and run its own social media campaigns through its members and supporters.
Many Our Revolution groups use language which explicitly emphasises their independence and their progressive commitment. Groups describe themselves as 'a nonpartisan progressive organization' (Our Revolution, 2019d) 'trans-partisan' (Our Revolution Lane County, 2019), a 'bipartisan grassroots movement' (Our Revolution, 2019n) 'a non-partisan political action group' (Our Revolution, 2019o) 'a multi-partisan network' (Washington Berniecrats Coalition, 2019). The independence of an organisation like Our Revolution is looked upon as important by sympathisers for the simple reason that 'grassroots driven organisations must be aligned with their supporters and donors or they will not be able to accomplish their goals' (Lenchner, 2015: 66). Maintaining some level of independence is vital for turning Sanders' support into 'the organisational strength necessary to realise' a left-wing programme to transform society (Fertik, 2016: 47). It certainly has the hallmarks of an independent organisation: with its own board, its status as a non-profit and its own staff 'made up of veterans and volunteers of the Bernie 2016 campaign and movement' (Our Revolution, 2019p). It has its own network of organisations -there are 500 registered groups around the United States -focused on organising in particular localities and communities around issues of concern to them (such as rent controls, use of public space and housing foreclosures). Our Revolution also maintains links to external organisations with similar goals in an attempt to enact a kind of 'tea party of the left' seeking to reimagine the practice of politics itself on less traditionally partisan lines (Aranoff, 2018: 8).
Nonetheless, Our Revolution's strategy has included working closely with and within the Democratic Party, providing endorsement and support for Democratic candidates in elections at various levels, although only those signed up to its aims and values (Aranoff, 2018). This, for some, is problematic. Even if justified as the only viable way of sustaining left-wing electoral campaigns (especially presidential ones), some activists assert that the goal must be a completely separate movement, to obviate the risk of absorption or diversion (see above). For them, the desire of left movements to attach themselves to the Democratic Party is historically 'the main explanation for its failure to build a sustained mass political alternative' and is a reason why some are wary of Our Revolution's strategy (Smith and Selfa, 2016: 4).
However, as others on the left have pointed out, the Democratic Party to all intents and purposes has no organisation to speak of, at least not in the European sense (Fertik, 2016;Hirsch, 2007;Schulman, 2016) which is in itself a strong reason, some would argue, for seeking to build a movement within it (Aranoff, 2018). The greater permeability and looseness of US party organisation means that independents and non-Democrats on the left (like Sanders himself) can easily enter into Democratic races anyway, much easier than it would be in the Labour Party, for example. This makes it possible for a wellorganised independent movement to maintain a distinct identity while working within a well-established party. In any case, Nina Turner, Our Revolution's President, claimed in a 2017 interview that working with groups and candidates outside the Democratic Party structures should not be ruled out either: Let's put the political affiliation to the side. If there is a Republican or a Libertarian or Green . . . that believes in Medicare for all, then that's our kind of person. If there's somebody that believes that Citizens United needs to be overturned, that we need the 28th amendment to the Constitution that declares that money, corporate money, is not speech and that corporations should not have more speech than Mrs. Johnson down the street and Mr. Gonzalez around the corner, then that's our kind of people. (Meyerson, 2017) While the lack of formal organisation means it is relatively easy to promote favoured candidates from outside the Democratic mainstream, it makes holding representatives to account once they have been elected much more difficult (Aranoff, 2018). How to ensure those who have benefitted from the movement's support remain faithful to its goals, then, is a significant problem.

Digital organising
Finally, essential to the capacity of movements like Our Revolution and Momentum to organise independently are social media and other inexpensive, usually web-based, organising tools. Digital technology is central to the way in which party-led movements have developed, helping to foster a 'party-as-movement mentality' (Chadwick and Stromer-Galley, 2016). Groups like Momentum and Our Revolution have brought these tools and mentality with them into the party arena, and used them to perform classic party functions like canvassing. In short, they are 'doing electoral politics differently' (Dennis, 2019: 5), bringing new approaches and techniques to the process rather than radically challenging the underlying strategy to win elections. The Bernie Sanders campaign and its subsequent movement benefitted from this (Lenchner, 2015: 66). Indeed, key figures in Sanders' campaign argue that it was central to the 'radical trust and community building' that was at the centre of a campaign designed 'to get as many people involved as possible' (Bond and Exley, 2016: 92).
Momentum members were more likely than regular party members to be politically active on social media and to attend public meetings (Poletti et al., 2016). Emulating organisations like 38 Degrees, online tools are part of the organisational infrastructure (Chadwick and Dennis, 2016), enabling members to initiate and vote on campaigns, propose constitutional amendments and challenge decisions made by the National Coordinating Group (Momentum, 2017a). Online organising has also supported effective campaigning: during the 2017 general election, Momentum launched 'My Nearest Marginal' App to help activists prioritise their campaigning, offer lifts or car shares and devote efforts to marginal seats (Dommett and Temple, 2018). It was used by over 100,000 people to locate battleground seats in order to campaign more effectively (The Week, 2017).

Conclusion
In this article, we have identified the party-driven movement as a distinct and potentially enduring organisational feature of the party landscape. Their emergence, in response to unrepresented claims or grievances, is made possible by overlapping networks between party and external movements representing those claims and the opportunities provided for these to coalesce within the party itself. In both cases, a unifying figure around which these movements and people can coalesce is important.
The effect of this has brought about changes to culture and organisation within US and UK parties that may yet prove to be relatively stable, but there are also tensions brought about by the movement's 'Janus strategy', which raises issues that must be resolved if this is to represent an enduring form of organisation. Are these new movements 'inside' or 'outside' the party and 'conventional' politics? What should be the focus of their strategy? And to what extent are they simply a part of the party or independent from it? There are significant differences between the US and UK party systems which makes it unlikely that they will have precisely the same form or effect. Nonetheless, they open up the possibility of an emergent hybrid organisational form fusing movement and party, with overlapping membership and close organisational and environmental connections between its two components (Della Porta et al., 2017;Tarrow, 2015).
The systemic context is clearly an important factor here. The examples we have used in this analysis are majoritarian, two-party systems. The dynamics of these systems are such that the possibilities of success for new parties are limited. Instead, movements need to attempt to influence or control the existing parties. This raises the question of whether party-driven movements are more likely to be limited to two-party systems and whether they could thrive in other settings. If so, what other forms might such movements take?
While both our case studies reflect left-wing social movement politics, similar instances could also be studied from right-wing party-driven movements. For example, the Tea Party's relationship with the US Republican Party could arguably be characterised in a similar way. We might also ask to what extent the UK Independence Party's (UKIP success up to 2016 could be ascribed to its strong associations with a broader (anti-European Union (EU)) movement which is now being fought over by the Conservatives and the new Brexit Party.
Such movements are also likely to face challenges that follow from their ambiguous status and contentious political role. First, a distinctive feature of party-driven movements is their 'insider/outsider' status which comes from an imperative to retain independence from the party while also operating within it. Such a precarious balancing act is difficult to maintain, and it is likely that movements will have to make tough choices between the two as they balance competing priorities. The risk on the one hand is in becoming detached from their movement origins and political base, or even completely absorbed by the party, thus losing their radical, outsider status. The party may be transformed by the movement, but the energy and participation it generated is lost. On the other hand, if in maintaining distance from the party mainstream, they lose the capacity to change the status quo they may become marginalised and impotent with similar outcomes. This is a significant challenge, closely related to an age old dilemma for democratic political parties, particularly of the left: how far to pursue the goal of power and risk breaking faith with their purpose and values.
Whether such movements can maintain this strategy is significant to the kind of longterm effect, if any, they are likely to have on parties and the party system more generally. While some of the innovations and changes that these movements have brought with them are well-established and could well be here to stay, we can only speculate on whether this foreshadows more radical developments or is merely a chapter in the slow evolution of parties as they adapt to the changing societies they seek to govern.