Party System Institutionalisation and the Structure of Affective Polarisation

Affective polarisation is rising across many democracies, often alongside processes of party system de-institutionalisation. In contexts where party identification and organisational loyalty are weakening, traditional parties lose their ability to structure political behaviour, making room for newer challenger parties and personalistic leadership styles. This paper explores how party system institutionalisation (PSI) relates to affective polarisation. Using original comparative survey data from five countries (Argentina, Chile, Italy, Portugal and Spain), we examine how citizens’ feelings towards (in- and out-) party leaders respond to variation in leader personalism and party-level characteristics. We find that while personalism significantly shapes both in-party affinity and out-party animosity in baseline models, these effects are asymmetric once PSI variables are introduced. While in-party affinity is highly contingent on party-level characteristics such as party type, out-party animosity remains more robustly tied to leader personalism. These findings show that PSI plays a crucial role in shaping partisan attachments, and that positive and negative partisan sentiment are structured by different party-level dynamics, supporting the view that they are distinct phenomena rather than mere opposites on a single attitudinal spectrum.