The informal rules of candidate selection and their impact on intra-party competition

While the literature highlights the relevance of informal rules for candidate selection, empirical research has mainly focused on formal rules and procedures. This article contributes to our understanding by investigating how the informal rules employed by political parties impact on intra-party competition. Using the example of district nominations in Germany, and based on a longitudinal mixed methods design, the inductive analysis reveals five central informal rules: the Incumbency Rule, the Information Rule, the House Power Rule, Fairness Rules and Power-sharing Rules. These rules shape the expectations and behavior of those involved in candidate selection and have a significant impact on various aspects of intra-party competition. They decrease the number of aspirants, reduce intra-party conflict and emphasize the role of local party leaders in organizing and controlling intra-party competition.


Introduction
Competition is a central aspect of representative democracy (e.g.Dahl 1971;O'Donnell et al., 1986).While intensive research on electoral competition has been conducted, intraparty competition has received less recognition.This is all the more surprising as intra-party competition is considered an important element of intra-party democracy (e.g.Rahat et al., 2008;Rahat and Shapira, 2017).The selection of candidates is a defining function of political parties and a crucial aspect of intra-party life making it an important arena of intra-party competition (e.g.Gallagher, 1988).Intra-party competition during candidate selection is also relevant as the "electoral game takes place in two arenas, not only between parties but also within them" (Hazan and Rahat, 2010; see also Carty, 1980;Schindler et al., 2021; see also the introduction to this Special Issue).It is an important part of the democratic process and strongly connected to representation and policy outcomes (e.g.Ascencio and Kerevel, 2020;Cross 2008;Zittel and Nyhuis, 2021).
There has been increased scholarly interest in studying the formal processes of candidate selection, yet the "informal rules of the game" (Norris, 2006: 92; see also Siavelis and Morgenstern, 2008) have received less attention despite their significance.Prior research on these informal rules has primarily focused on their gendered effects (e.g.Kenny and Verge, 2016;Van Dijk, 2023) and the interaction between formal and informal rules (e.g.Cross, 2018;Kelbel, 2020;Meserve et al., 2017).However, little attention has been paid to how these informal rules affect intra-party competition.
Research on political competition shows that informal rules such as fairness and power-sharing rules are prevalent in the electoral arena and parliament.They are perceived as highly relevant for the stability and functioning of the organizations and for democracy as they limit competition between parties and factions (e.g.Katz and Mair, 1995;O'Donnell et al., 1986).It is likely that similar informal rules are adopted in the process of candidate selection, as excessive competition may threaten the party's unity and vote-seeking goals.Therefore, the research question motivating this study is: What are the informal rules employed by political parties during candidate selection and how do they impact on intra-party competition?A longitudinal mixed-methods research design focusing on district selections in Germany in 2009 and 2021 was used to investigate this research question.While Germany is known for its detailed legal and party regulations (van Biezen and Piccio, 2013), research also indicates the existence of informal rules (Reiser, 2014a(Reiser, , 2019)).The research strategy combines a quantitative analysis on the level of intra-party competition, and face-to-face interviews with party officials and (successful and unsuccessful) intra-party aspirants.This design allows inductive generalizations to be made about informal rules and their impact on intra-party competition.By that, the article contributes to the symposium by focusing on the role of political party for intra-party competition at the nomination stage.

Theoretical framework: informal rules and competing logics of candidate selection
There has been growing interest in intra-party competition and candidate selection in the last few years (e.g.Coller et al., 2018;Cross and Katz, 2013;Gallagher and Marsh, 1988;Hazan and Rahat, 2010).One important conceptual approach is the supply and demand model of recruitment (Norris and Lovenduski, 1995).According to this model, the process of candidate selection involves interaction between the aspirants aiming to run for office and the gatekeepers who make the selection.The interaction between supply and demand is embedded in a wider framework of opportunities that includes macro-institutional factors (e.g. the electoral system) and the party's rules and procedures.These act as a "funnel of causality" (Norris, 1997, 100) through which individuals must pass in order to be nominated by the party.
With the focus on informal party rules, this article thus examines an important aspect of the framework of the recruitment process.Rules are important since they shape the incentives, expectations, and behavior of the selectorate and the aspirants, thus structuring the process and outcome of candidate selection.(Helmke and Levitsky, 2004).Research has revealed a general trend in the rules towards the democratization of candidate selection (e.g.Bille 2001;Hazan and Rahat, 2010).However, empirical studies have largely focused on analyzing the formal and "written rules of the game" (Cross, 2008;Sandri et al., 2015;Shomer, 2014, Siavelis andMorgenstern, 2008: 5).This includes both legal rules (e.g.van Biezen and Piccio, 2013) and written party statutes (Helmke and Levitsky, 2004).
Informal rules by contrast are "socially shared rules, usually unwritten, that are created, communicated, and enforced outside of officially sanctioned channels" (Helmke and Levitsky, 2004: 727; see also Chappell and Mackay, 2017;Siavelis and Morgenstern, 2008 for similar definitions).These informal rules and norms are learned and adapted gradually and mainly unconsciously by (new) party members in the process of socialization (e.g.Dickinson, 2018;Reiser et al., 2011;Rush and Giddings, 2011).Their degree of institutionalization can vary (Siavelis and Morgenstern, 2008): Rules are regarded as highly institutionalized if they are widely known, recognized, habitually accepted and enforced through sanctions and rewards within the organization.Less institutionalized informal rules are less widely recognized and accepted, i.e. they are regularly challenged and heavily debated within parties (see also Bjarnegård and Kenny, 2015;Chappell and Mackay, 2017).
The important role of informal-and particularly highly institutionalized-rules for candidate selection has been widely recognized (Gallagher and Marsh, 1988;Hazan and Rahat, 2010;Norris, 2006).However, due to technical challenges and the need for field-intensive and timeconsuming methods to study such informal practices (Mughan et al., 1997), they have only recently been the subject of increased empirical research.One important strand of literature has studied the gendered effects of these informal rules and reveals how parties intentionally and unintentionally employ informal practices that affect the outcome of candidate selection and explain the underrepresentation of women in parliament (e.g.Kenny and Verge, 2016;Colley and Van Acker, 2020;Gatto and Wylie, 2022).Another strand of research examines the interaction between informal and formal rules showing that informal rules are not always congruent with the formal rules in place, but are sometimes supplementary and rather interact or even compete with them (Cross, 2018;Kelbel, 2020;Meserve et al., 2017;Vandeleene and Van Haute, 2021).It is therefore essential to consider both types of rules in order to understand the strategic choices and incentives behind the political behavior of the actors involved (Helmke and Levitsky, 2004).
Despite this increase in research, our knowledge of the impact of these rules on intra-party competition is still limited.The literature on political competition stresses the highly functional nature of the informal rules that structure and regulate political competition.Both intra-party and inter-party competition is characterized by uncertainty and the risk of losing.In relation to inter-party competition, Strøm (1992: 390) notes that "the more intense the competition, the more acute the threat of failure.(…) So the toleration and protection of temporary political losers (oppositions) have been critical to the establishment of democracy".
It has been suggested that informal rules and strategies are central to structuring competition between parties in parliaments and the electoral arena (e.g.rules of powersharing and fairness rules; see e.g.Borchert, 2003;Katz and Mair, 1995).Similarly, O' Donnell et al. (1986: 41) indicate that these rules, which "tend to reduce competitiveness as well as conflict", have been crucial in processes of democratization (see also Levitsky and Ziblatt, 2018 on the consequences of the erosion of these rules for democracy).
In line with this argumentation, it is important to study whether parties also employ such rules in the process of candidate selection and whether they influence intra-party competition.It has been stressed that intra-party competition is a key element of both intra-party democracy and democracy at the state level (e.g.Rahat et al., 2008;Cross, 2008).Candidate selection is one of the defining functions of a political party and a central arena for internal power struggles (Gallagher, 1988;Hazan and Rahat, 2010;Norris 2006).But if intra-party competition is too intense and conflictual, it may put the strategic goals of party unity and vote-seeking at risk (Ascencio and Kerevel, 2020;Pedersen and Rahat, 2021).It can therefore be assumed that parties seek to promote party unity by limiting and structuring competition, for example, by employing fairness rules and expectations of loyalty towards the party and party leadership.Vote-seeking can be negatively affected by overly intense intra-party competition.As Michels (1911) argues, a high level of intra-party competition can not only weaken party unity but also the chances of the party in the electoral contest (see also e.g.Greene and Haber, 2015;Lehrer et al., 2022).Therefore, it can be assumed that parties strive to reduce intensity of intra-party competition since candidate selection takes place shortly before the election campaign and the elections.
Even though norms of solidarity and loyalty have been studied within political parties and parliamentary groups (e.g.Bolleyer, 2009;Hirschman, 1970;Panebianco, 1988), there has been little examination of how informal rules structure and possibly limit intra-party competition during candidate selection.The aim of this study is thus to examine the informal rules parties apply in the process of candidate selection and how these rules affect intra-party competition.

Intra-party competition in Germany
Germany provides an interesting case for studying informal party rules for intra-party competition and has been described as the "heartland of party law" (Müller and Sieberer, 2006: 435) due to its detailed legal regulations for candidate selection (van Biezen and Piccio, 2013).But there are also studies indicating the existence of informal rules for candidate selection.These refer to the rule on not challenging the incumbent and to rules that guarantee group representation in balancing the state party lists (Baumann et al., 2017;Ceyhan, 2018;Reiser, 2014a;Weßels, 2016; for a first attempt to study them at the district level see Reiser, 2019).
Candidate selection is highly decentralized in Germany's mixed-member electoral system (Klingemann and Weßels, 2001;Manow, 2015).There are two independent forms of candidacy with different selectorates, the district candidacy and the candidacy on the state party list.Candidates may, however, run for both simultaneously.Double candidacies are prevalent today as about 90 percent of MPs run both in the district and on the state party list (see Baumann et al., 2017;Manow 2015).Studies also show that a district candidacy is de facto a precondition for a good or promising spot on the state party list (e.g.Schüttemeyer and Sturm, 2005;Ceyhan, 2018;Reiser, 2014a).This points to the high relevance of district nominations, even in cases where the local mandate cannot be won.
District candidates are typically nominated at either a meeting of the party membership in the constituency or by a meeting of delegates elected by the members of the local party branches in the district (see Tables A3 and B3 in the Supplementary Material).It is important to note that electoral districts and party branches are often not congruent: in only 32% of cases, only one county party branch is responsible for the nomination.In the majority of electoral districts, members or delegates of two to four county party branches jointly nominate the candidate (see Supplementary Tables A2 and B2).

Research design, methods and empirical basis
Researching informal rules is challenging from a methodological and empirical perspective.It is difficult in terms of accessibility because "parties do not like the odours of the electoral kitchen to spread to the outside world" (Duverger, 1959).Since informal rules are not written down and partly unconscious and internalized, it is very difficult to chart them using conventional survey methods (Mughan et al., 1997).An inductive research strategy based on a longitudinal mixed-methods design was employed to address this challenge.The analysis combines two studies conducted to investigate the informal rules used by political parties during candidate selection in constituencies for the 2009 and 2021 federal elections in Germany.
The 2009 study is based on an analysis of 32 candidate selections in electoral districts.The sample comprises selection processes of four parties: the Social Democrats (SPD), the Christian Democrats (CDU), their Bavarian sister party Christian Social Union (CSU), as well as the Left party in East Germany, as only these parties had the chance to win district seats. 1 For case selection, in a first step, data on intra-party competition was collected for all 661 districts of the four parties.In a second step, for each party, a disproportionate stratified samplingbased on the two criteria degree (number of intra-party aspirants) and type (with or without incumbent) of intra-party competitionwas used to study informal rules in different settings for each party (see Tables A1, A2 and A3 in the supplementary material, see also Reiser, 2014b).
A mixed-methods design was used to derive the informal rules employed by the parties.Semi-structured in-depth interviews with all actors involved in the process (local party leaders, successful and unsuccessful intra-party aspirants) constitute the core of the analysis.143 interviews were conducted between December 2009 and October 2010 (return rate of 78.1%) from the 183 party actors targeted.Additionally, 35 local journalists in these districts were interviewed to include an outside perspective.
The 2021 study is based on 20 candidate selections.In contrast to the 2009 study, this study does not just include the CDU, CSU, SPD and Left Party, but also the other three parties that were represented in the Bundestag as factions in 2021 (the Green Party, the Liberal Party and the AfD).The main reason for this is the changes of the party system and voting behavior.All parties (with the exception of the Liberal Party) won district seats in the 2021 federal election.
A random sample of 50 electoral districts was drawn from the 299 constituencies in Germany for the case selection.Data on intra-party competition was collected for each of the parties (SPD, CDU or CSU, Greens, Left, Liberals, and AfD).As with the 2009 study, a disproportional stratified random sample was taken for each party based on two criteria (with or without incumbents; number of aspirants; see Tables B1, B2, and B3 in the supplementary material).As with the 2009 study, the core of the study is face-to-face interviews with party actors in the selected electoral districts.36 interviews were conducted in September and October 2022 (response rate: 35.9%) from the 101 party actors (local party leaders, unsuccessful and successful aspirants) targeted.Since all but one AfD member refused to participate, the analysis only includes selections of the six remaining parties (CDU, CSU, SPD, Green Party, Liberals (FDP) and the Left Party).
Although cases, samples and the database of the two studies from 2009 and 2021 differ to some extent, this research design allows the informal rules used by all relevant political parties in the processes of candidate selection in Germany and their impact on intra-party competition to be examined.A comparison of the results from 2009 and 2021 for the CDU, CSU, SPD, and Left Party also enables their stability and degree of institutionalization to be studied.

Empirical analysis
The inductive analysis of the nomination processes in the electoral districts for the Federal Elections 2009 and 2021 reveals five informal rules.
First, the Incumbency Rule is a very important and wellestablished informal rule.This means that, at the district level, an incumbent is not openly challenged during candidate selection."There is the old principle of the primacy of the incumbent-unless he is unacceptable" (I2009-79; see also e.g.I2009-21; I2021-14).Challenging an incumbent at the nomination conference is regarded as "a lack of solidarity" (I2009-2) and "indecent behavior" (I2021-I4).It is evident from the interviews that a violation of this rule is met with sanctions which are not only limited to the current candidacy but can also have long-term consequences: "He has disqualified himself.I'm sorry, because he has a good profile and is committed.It's very unfortunate from the point of view of the party organization.We can't allow promising political talents to be lost.But because of his behavior, he won't have the chance of being nominated for public office in the future" (I2009-77).
There are two exceptions to this rule: If there has been long-term criticism of the incumbent's commitment in the district or he/she is perceived as being too old.But even in these cases, party leaders usually strive for an informal compromise in order "not to damage the incumbent publicly" (I2009-4).This usually involves a "voluntary" withdrawal of the incumbent in order to avoid an open intra-party competition at the nomination conference (e.g.I2021-14; I2009-67).This is in line with research showing a strong and negative effect of incumbents on intra-party competition in German districts (Baumann et al., 2017;Reiser, 2014b;Schindler et al., 2021;Weßels, 2016).This rule applies to all political parties apart from the AfD 2 (see Tables A1 and B1 in the supplementary material).It is also noteworthy that political ideology, party type, the mode of election of the incumbent at the last election (direct or via list), and chances of success in the constituency have little or no influence on the relevance and compliance to this rule.The incumbency rule thus protects incumbents and minimizes uncertainty in their political careers (Borchert, 2003).At the same time, this rule acts as a barrier for new aspirants, thus constraining intra-party competition.
The Information Rule is a second rule consistently applied during candidate selection processes in constituencies.It requires aspirants to inform the leaders of their local party branch and the county party of their intentions before publicly announcing their candidacy (see also the House Power Rule).This rule is considered a crucial element of party hierarchy and loyalty, as demonstrated by the following two statements: "The young man did not seek my opinion prior to announcing his application.This is a basic requirement and it is strategically beneficial to seek my advice as the chairman of the county branch first" (I2009-5; see also I2009-70; I2021-18).
"I failed to ask my local party chairman for his support before announcing my candidacy.In retrospect, I know that this is an unwritten law.Afterwards, everyone said 'How can you run if you don't have the support of your local party chairman?' (...) In their eyes, my behavior reflected a lack of party solidarity" (I2009-140).
Violation of this rule was sanctioned in all cases studied, mainly by not receiving support from party leaders in the intra-party competition.Since their support is a key resource and often an important prerequisite for a promising candidacy, this clearly reduces the chances of winning the intraparty race.And indeed, in all cases examined, the aspirants lost the intra-party competition due to lack of party leader support (e.g.I2021-36).
According to the interviewees, the rule predominantly has two functions.First, it enforces the organizational goals of party unity and hierarchy by ensuring the important role of local party leadership in organizing and controlling intra-party competition in decentralized candidate selection (see also Detterbeck, 2016).Second, it aims to guide aspiring candidates.Local party leaders regularly advise young aspirants not to run in the upcoming nomination because they would not (yet) meet the requirements deemed crucial for nomination (e.g.long-term commitment in local politics) or would violate informal rules (e.g. the incumbency rule).In this way, local party leaders act as important agents for socialization, conveying the expectations of the party organization, the (formal and informal) rules and the sanctions for violating them (see Dickinson, 2018;Reiser et al., 2011).This, however, restricts the openness of candidacy and limits intra-party competition.
The House Power Rule is the third informal rule which implies that the support of the local party branch is a prerequisite for a successful intra-party candidacy.This means that, particularly in safe and promising SPD, CDU, and CSU districts, each local party branch only sends one candidate to the formal nomination convention.When more than one party member seeks nomination, preselection usually takes place at the local party branch.As an example, one aspiring candidate stated: "In my case, there were four of us at the local party branch.During the presentation, we were asked what we would do if we were not preselected by the local party branch.And if you don't declare that you will withdraw your candidacy should this happen, you have already lost" (I2009-80; e.g.I2021-17).
There is an expectation that the candidate will accept selection made by the local branch and not pursue application if they lose (I2009-30; I2009-81; I2009-30; I2021-41).A violation of the rule is rated as "disloyalty to the party" (I2009-19; I2009-60; I2021-10).De facto, this rule leads to a two-stage process of candidate selection at the local party branch and then in the electoral district.It also reduces intra-party competition at the actual nomination conference.
Intra-party candidate selection is also structured by a number of Fairness Rules that address the behavior of aspirants during the selection process.Research has shown that campaigns to mobilize and persuade members of the selectorate can be extremely intense, in particular in safe districts (e.g.Höhne, 2013).The fairness rules are aimed at taming the level of conflict.
"One of the rules of the game is not to harm any of your competitors.There should be no personal attacks, no material battles and no broken pieces left behind.These rules make it possible to reunite the party after the selection process and run a successful electoral campaign in the district" (I2009-40; see also I2009-80; I2009-102).
Another fairness rule is that candidates withdraw their application before the official nomination conference if they stand no chance of winning the competition.This applies to the cases of preliminary voting in the local party branches (see House Power Rule) as well as cases in which favorites emerge during the intra-party campaign.Aspirants are expected to withdraw their application so as not to influence the intra-party competition between favorites: "You have to be careful not to take votes away from the two favorites.You are expected to be fair.I wanted to be fair so I withdrew my application before the nomination conference" (I2009-19; similarly, I2009-44).
Losers of intra-party competitions are also expected to accept the result of the competition and to actively support the electoral campaign of the district candidate.At the same time, the fairness rules serve the function of protecting losers of intra-party competitions (I2009-20; I-2009-50) in order to prevent them from withdrawing from active party work or even leaving the party in response to defeat.This confirms earlier findings from Canada (e.g.Cross and Pruysers, 2019).
Despite these fairness rules, over a third of nomination processes have witnessed violations.These receive weaker sanctions compared to other informal rules.However, they still tame intra-party competition and encourage party unity during and after candidate selection.A positive and unified party image in the eyes of the public is considered crucial to winning, especially as candidate selection occurs just before the elections.
"How can I organize an electoral campaign that demonstrates party unity despite an intense intra-party contest?Competition is valuable, but it should be regulated to avoid harming the party.It shouldn't result in permanent damage" (I2009-2; see also I2009-55; I2009-80; I2021-21).
The study also reveals the existence of informal rules for power sharing.The highly decentralized selection method used in single-member constituencies in Germany makes ticket-balancing 3 less likely to occur as the local party branches determine candidate selection with no (or minimal) influence from higher party levels (Detterbeck, 2016).Nevertheless, the study shows that informal rules for powersharing do exist at the district level.
First, there are rules of power-sharing between county branches.In approximately two thirds of the electoral districts, multiple county party branches jointly nominate the candidate (see Tables A2 and B2 in the supplementary material).In some cases, the county branches take turns nominating the district candidate.In others, one county branch sends the district candidate for the national parliament while the other county branch can appoint the candidate for the state parliament (see I2009-69; I2009-140; I2021-4).
Second, there are also rules of power-sharing between different factions, predominantly in larger cities, where the county branch is responsible for nominating two or more district candidates: "I belong to the left-wing faction of the party.Traditionally, the right-wing faction has the informal right to nominate a candidate in this district.The left-wing faction has the informal right in the neighboring constituency.When I announced my candidacy, I immediately got into trouble with the local party leader.The candidate of the neighboring constituency was also pissed off because I violated this informal agreement.After that, many clearly distanced themselves from me (…).Hence, the balance between the left-and right-wing factions is extremely important to the party" (I2009-22).
These power-sharing rules aim to reduce "internal power struggles" (Gallagher, 1988) and promote party unity.However, they also limit the openness of the nomination process by effectively excluding candidates from other county branches or factions from competing within the party.As illustrated in the examples above, these rules (e.g.alternating between party branches, allocation of state and national parliament's candidacy to the different party branches) vary widely among parties and districts and depend on the specific party's power structure in the electoral districts.These power-sharing rules are less common than the other informal rules, and the analysis revealed their presence in only around onethird of the districts examined.However, if they do exist, they are usually highly institutionalized and strictly enforced.

Informal rules: differences by party, competitive context and over time
Remarkably, the analysis reveals a high level of generalizability among the regulations governing political parties and constituencies although some minor differences occur.
With regard to party type and party ideology, the analysis indicates that the informal rules are most strictly enforced within the CDU, CSU and SPD.This confirms previous research that catch-all parties have more highly institutionalized informal rules for the nomination of state party lists (Reiser, 2014a).The rules also exist in the other parties but seem to be less institutionalized in the Liberal and the Green parties.Green Party interviewees in particular stress that rules related to party hierarchies are less important "because the idea of grassroots democracy continues to shape the processes within our party" (I2021-8; see also I2021-11).This confirms studies that reveal the initial anti-hierarchy and grassroots democracy characteristics of the Green Party are still present today (Poguntke 2017).
The competitive context of the electoral district also appears to have an impact.The analysis shows that when there is an opportunity to win a mandateeither in the district or as a result of double candidacy via the state party listcompliance with the rules is perceived as crucial.In districts where candidates have little chance of being elected, there is some variation in the perception of compliance and enforcement.Aspirants mainly report that they "stick to the rules" (I2021-10) and "do not risk trouble" (I2009-4) as there is nothing to gain.Party leaders, however, sometimes indicate that they enforce rules less strictly so as not to risk "conflict in the party branch when nothing is at stake" (I2021-5; see also I2021-26).
Comparing the nomination processes in 2009 and 2021 reveals that the informal rules have remained largely unchanged over time.This stability is striking considering the significant changes to the party system, electoral behavior and the democratization of intra-party processes (Coller et al., 2018;Borz and Janda, 2020;Hazan and Rahat, 2010).Most rules have barely changed for decades with some dating back to the 1950s (e.g.I2009-55; I2021-2; see also Kaack 1969).This high level of institutionalization suggests that these informal rules have become deeply ingrained in the parties' internal workings.
The impact of the Covid-19 crisis on the established compliance to these rules during candidate selection for the Federal Elections 2021 is therefore all the more significant.Due to pandemic containment measures, party meetings were held digitally which affected communication and consequently the enforcement of the rules.Some interviewees noted that the use of digital tools weakened solidarity and loyalty among members and that face-to-face meetings were necessary for maintaining commitment to the party and the rules (e.g.I2021-2).This also affected the process of socialization for new members, with a third of the interviewed party leaders noting that the lack of informal meetings impeded these processes: "They do not really know the rules yet and they lack norms governing loyalty.[...] This was also obvious in the nomination process.While X [an aspirant] withdrew his candidacy out of loyalty, the newer members did not follow this rule and did not withdraw their applications" (I2021-4).
However, most interviewees expressed the belief that the pandemic would not have a lasting impact on the informal rules and that the established socialization processes could be made up for now that in-person events were able to take place again.

Informal rules and their effect on intra-party competition
The inductive analysis reveals that informal rules have a significant effect on several dimensions of intra-party competition during candidate selection.
First, several of these rules de facto limit the number of competitors in the candidate selection process and at the formal nomination convention.The Incumbency Rule discourages candidates to run against an incumbent.The rule helps to explain why incumbency hampers intra-party competition (Reiser, 2013;Schindler et al., 2021;Weßels, 2016) and why non-incumbents rarely win (Hazan and Rahat, 2010).
The Information Rule, the House Power Rule and the Power-sharing Rules de facto restrict the number of aspirants and the openness of candidacy, e.g.due to further eligibility requirements of aspirants (see also Norris and Lovenduski, 1995).This contradicts the regulation in the Electoral Law which stipulates that "any voting participant in the convention" can propose a candidate or put himself forward at the nominating conference (Section 21 of the Electoral Law).In this way, the informal rules are less inclusive than the formal rules.This supports the observations on patterns in political parties' candidate selection for the European Parliament made by Meserve et al. (2018) and Kelbel (2020).
Second, some of the informal rules reduce the level of conflict in the process of candidate selection.Power-sharing rules establish a balance of power between local party branches and intra-party factions and pacify intra-party conflicts by structuring and channeling intra-party competition and fostering party unity.Similarly, informal fairness rules promote fairness, unity and solidarity within the party during and after candidate selection.This is particularly important as candidate selection takes place just before an election and tough intra-party competition would risk the electoral goals of the party (Michels, 1911;Panebianco, 1988).
Third, the rules have an impact on the organization of intra-party competition.Section 21 of the Electoral Law states that the nomination convention decides who will run for candidacy in the electoral district.However, informal rules de facto often lead to a multistage process in which preselections are held at local party branches and only the winners run for candidacy at the formal nomination convention (House Power Rule; see also Schindler et al., 2021).This is also evident from a quantitative analysis of the 2009 Federal Elections which showed that at least 24% of the nomination processes involved at least one applicant withdrawing their application before the convention due to preselections (Reiser, 2014b).The informal rules also emphasize the crucial role of local party leaders.The House Power and Information Rule stress the importance of loyalty and deference towards the party leadership and ensure the local and regional party leadership's role in organizing and controlling intra-party competition in decentralized candidate selection (see also Andeweg and Thomassen, 2011;Detterbeck, 2016).

Conclusion
This article has examined the informal rules that political parties employ in the process of candidate selection and how these rules impact on intra-party competition.Despite the relevance of intra-party competition as a central dimension of (intra-party) democracy (e.g.Rahat et al., 2008) and the importance of informal practices for the process and outcome of candidate selection (e.g.Bjarnegård and Kenny, 2015;Norris, 2006), there has been limited research on the effects of these rules on intra-party competition.
The initial assumption was made that informal rules play a role in structuring and limiting intra-party competition.This is likely given that research has shown the important role of such informal rules for political competition at the state level (e.g.O'Donnell et al., 1986;Strøm, 1992).Conflictual intra-party competition can also threaten a party's unity and electoral success (e.g.Andeweg and Thomassen, 2011), meaning it is likely that informal rules have been established to regulate intra-party competition.
Using the example of district nominations in Germany for the Federal Elections 2009 and 2021 and based on a longitudinal mixed methods design, the inductive analysis reveals five central informal rules: the Incumbency Rule, the Information Rule, the House Power Rule, Fairness Rules and Power-sharing Rules.The findings reveal that these informal rules are crucial in shaping the expectations and the behavior of the actors involved in the process of candidate selection.They have been in place for a considerable amount of time (see Kaack, 1969) and, with the exception of the Fairness Rules, are highly institutionalized as demonstrated by their wide recognition and acceptance within the parties and their enforcement through sanctions.
The differences between party type and ideology and the competitive context in the districts are relatively small indicating a high degree of generalizability among German political parties.These findings also align with studies in other countries which observed rules for incumbency and power sharing (e.g.Van Dijk 2023;Hazan and Rahat, 2010).Evidence of fairness and loyalty rules within parties, especially in parliamentary groups, has also been noted (e.g.Bolleyer, 2009;Hirschman, 1970).Further research is needed to study which and why informal rules are employed across countries and within different party systems.
The present study reveals that these rules have a significant impact on several dimensions of intra-party competition during the process of candidate selection: First, several of these rules effectively limit the number of aspirants and the degree of intra-party competition.The Incumbency Rule discourages challenging incumbents and reduces the uncertainty of political careers (see also Borchert, 2003;Katz and Mair, 1995).The Information Rule, the House Power Rule and the Power-sharing rules restrict the formal openness of candidacy with informal pacts that hinder certain aspirants from running or add eligibility requirements.Second, these informal rules reduce intra-party conflicts through power-sharing rules (see also Poguntke, 2017) or by promoting fairness rules between competitors and their supporting groups.Third, these rules also have an impact on the organization of intra-party competition.Preselection at local party branches effectively turns candidate selection into a multistage process involving distinct selectorates at successive points in time (see Kenig et al., 2015).The House Power and the Informal Rule also secure the crucial role of local party leaders in organizing and controlling intra-party competition in decentralized candidate selection.
The interviewees indicate that the purpose of these rules is to organize and restrict intra-party competition so that the two main objectives associated with selecting candidatesmaintaining party unity and vote-seekingcan be achieved.The informal rules promote party unity by encouraging solidarity towards the party and deference towards the party leadership (Andeweg and Thomasson, 2011;Panebianco, 1988).Parties also have a strong desire to appear united in public as this increases their chances of winning elections.Too much conflict within the party risks the party's electoral chances (e.g.Michels, 1911;Greene and Haber, 2015).
This finding also contributes to the current debate on the personalization of politics and the trade-off between party loyalty and electability during the process of candidate selection (e.g.Ascencio and Kerevel, 2020;Pedersen and Rahat, 2021;Reiser, 2022).As compliance with (most of) these informal rules is a basic prerequisite for a promising candidacy in the selection process, this tends to favor aspirants who have already been active in the party for a while.As the rules demand solidarity towards the party and deference to the party leaders, this might also apply to their future behavior in parliament.The results indicate that, even when electability is the primary concern in selecting a candidate, the informal rules ensure a certain level of party loyalty.
The findings also offer new insight into the research on selection criteria and descriptive representation.Informal rules tend to favor incumbents and those with a long-term record of engagement in the party.As such the rules are closely interlinked with the selection criteria (see e.g.Berz and Jankowski, 2022;Vandeleene and Van Haute, 2021) and may help explain gendered effects of candidate selection (e.g.Van Dijk, 2023).The rules also tend to focus on territorial local representation, e.g. by employing power-sharing rules between party branches.This confirms previous research which has shown that party selectorates prioritize territorial representation over social representation during decentralized candidate selection in electoral districts (e.g.Childs and Cowley, 2011).This results in a low proportion of women being nominated in safe districts (e.g.Davidson-Schmich, 2016).These informal norms contribute to a better understanding of the reasons behind the underrepresentation of women in parliament and confirm studies highlighting the role of these informal practices (e.g.Bjarnegård and Kenny, 2015).
Although this analysis primarily focuses on informal rules, the findings also contribute to research on the interactions between de jure and de facto party rules (e.g.Bjarnegård and Kenny, 2015;Meserve et al., 2017).Informal rules seem to partially supplement formal rules by regulating areas that are not covered by formal regulations, particularly with regard to fairness and loyalty (see for similar informal rules in parliamentary factions, e.g.Dickinson 2018).But informal rules are also less inclusive than formal rules, particularly with regards to candidacy and the selection process.These findings align with previous research (e.g.Kelbel, 2020;Van Dijk, 2023) and suggest that informal rules may to some extent contradict the trend towards democratization of political parties (e.g.Hazan and Rahat, 2010).
The findings of the analysis also contribute to the literature on the impact of digitalization on political parties (e.g.Barberà et al., 2021;Pérez-Nievas et al., 2018).The COVID-19 pandemic has necessitated the use of digital tools by established parties.The reliance on digital tools and the lack of face-to-face interaction in the process of candidate selection affected compliance with informal rules, particularly in terms of rules of solidarity and loyalty.Further research is needed to study whether this has longterm or only temporary consequences on compliance with these informal rules.

Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.