The second part of the book investigates the implementation of the policy. As far as preventive surveillance is concerned, at its core lay the country-specific recommendations on the macroeconomic policies of the member states. These recommendations are the object of intense negotiations between the Commission and the Council. Why are they a matter of bargaining? What shapes the Council’s propensity to modify the Commission’s proposals and what affects their strengthening or weakening? This chapter employs bargaining and compliance theories to address these questions. Analyzing the recommendations issued between 1999 and 2019, it shows that the Council is rather active in modifying the Commission’s assessments and strengthens four-fifths of the recommending provisions that it decides to modify. Economic and supranational factors dominate this process. Governments balance the pressures originating from the bargaining dynamic within the Council with the need to preserve policy credibility and effectiveness in the face of noncompliance and worsening economic conditions.

Chapter 2 presents the book’s main argument about how party rules shape membership. Previous literature is split in its portrayal of party members – some scholars describe members as extremist ideologues, whereas others depict them as partisan loyalists. To reconcile these competing views, Chapter 2 develops a spatial model of membership in which members receive utility from government policy and party proximity, as well as features of party membership unrelated to ideology. The model demonstrates that party rules play a pivotal role in shaping a party’s overall membership level and distribution. The model predicts that decentralized parties attract more members than centralized parties, all else equal. However, decentralized parties’ members should be more ideologically extreme than their counterparts in centralized parties.

Chapter 1 sets the stage by comparing leadership elections in the two major UK parties following the Brexit referendum. While Conservative members of parliament acted swiftly to replace their leader, Labour was unable to follow suit, leading to an unprecedented internal crisis. These divergent paths, Kernell argues, can best be explained by attention to party rules. After briefly extending the comparison to discuss party rules in several other countries, Chapter 1 summarizes the book’s core arguments and the formal model, introduces the evidence, and provides a roadmap for the rest of the book.

Chapter 3 guides the reader inside parties by examining how candidate nominations, leadership selection, and policy platforms operate in modern democracies around the world. Kernell examines variation among these rules both within and across countries, as well as over time, and proposes a coding methodology for defining the degree of membership influence in each of the three primary dimensions. The chapter also discusses case selection and data collection.

Chapter 5 builds on the observational findings from the previous chapter to test the hypotheses using two survey experiments performed on a sample of British Labour voters. The first experiment manipulates the selective incentives available to members by changing the cost of joining. Not surprisingly, people are more interested in joining when fees are low. The second experiment manipulates the party’s instrumental incentives by stating members can (or cannot) select party leaders and parliamentary candidates, as well as attend events where they may formally participate in determining the party’s future policy direction. The findings support the hypotheses generated by Chapter 2’s formal model: decentralization increases membership, conditional on voter-party alignment.