Differentiation and Compromise: Parliamentary Strategies in Multilevel Settings

Political parties in parliamentary democracies face a fundamental strategic tension between differentiation and compromise. While parties must distinguish themselves from competitors to maintain and expand their electoral base, governing often requires compromise with those same competitors. Existing research has emphasised how parties use parliamentary behaviour to signal differentitation while remaining viable coalition partners (Martin and Vanberg, 2008, 2011; Fortunato, 2021). Yet, much of this literature has focused narrowly on coalition partners within government, leaving support parties and multilevel legislative dynamics comparatively underexplored. This paper argues that parliamentary amendments constitute a central tool through which parties strategically seek to differentiate from their partners in cabinet or as support parties. Crucially, I argue that this behaviour varies systematically according to a party’s relationship to the executive and its perceived proximity to the executive by voters. To test these claims, this paper uses and expands the dataset compiled by Palau et al. (2025) which includes over 90,000 amendments in the Spanish Congreso between 1996 and 2023. I extend this dataset to include the parliamentary status of being in opposition, a support party, a coalition partner or the PM’s party. Furthermore, I include regional parliaments to assess the potential variation in behaviour in multilevel settings.