Priming Polarisation: How Parties Use Divisive Issues to Concretise Voter Identities and Mobilise Their Supporters

The rise of political polarisation is of great concern to scholars of Western democracy. Polarisation promises to undermine support for democratic norms, while upending the established liberal order. Surprisingly however, little if anything is established about how polarisation fits into existing theories of electoral competition. This paper attempts to bridge this gap by looking at the effects of voter polarisation from a multidimensional issue competition perspective. In short, I theorise that the salience of a polarising issue primes not only the issue itself, but also the identities of the groups which are polarised. Therefore, parties should focus primarily on issues which are polarised according to party support (party polarisation), in order to mobilise supporters around a shared party identity. This theory is put to a quantitative test in five Western European elections held from 2017-18, taking data about voter preferences and party issue attention (on Twitter) from the Issue Competition Comparative Project (ICCP). As predicted, the analysis finds that party polarisation increases the rhetorical responsiveness of political parties to their own supporters. Meanwhile, issues where polarisation is uncorrelated with party support (issue polarisation) generally received less attention. A provocative normative implication of these findings is that party polarisation might even improve the representative quality of democracy, despite its well-documented negative effects.