Chapter 5 examines how collaboration varies across members. Nearly every member of Congress collaborates to some degree, but there is significant variation with some members coauthoring one or two policy proposals in a Congress and others forming relationships with fifty colleagues or more. Examining this variation reveals clear patterns in the characteristics of the most and least collaborative members and illustrates how collaboration is a function of a member's incentives and opportunities. Members who interested in policymaking are incentivized to collaborate more, and those who are well connected in Congress have more opportunities. Members representing competitive districts are more likely to collaborate with the other party, while those representing partisan districts work with their co-partisans. Consistent with social exchange theory, members collaborate to support their electoral and policy goals but are constrained by their ability to identify a worthwhile partner.

This chapter provides the theoretical underpinnings for an analysis of the impact made by populist radical right parties in local government. This theoretical framework is grounded not just in theories particular to the party family, but also ones more general to the analysis of party politics and institutions. Four main questions are addressed. First, regarding the policy goals of the populist radical right: what do they want? Second, regarding partisan influence over government policy, do parties matter – even in local government? Third, regarding the mainstreaming of the populist radical right, are they tamed by power? And fourth, regarding the strategic uses of local government made by parties, are such localities laboratories of radicalism? Before the subsequent chapters analyse the different routes taken by populist radical right-led local governments in Western Europe, this chapter provides several explicit expectations for how their impact is likely to vary cross-nationally according to two main factors: institutional constraints and central party strategies.