Framing Effects on EU Public Opinion Formation: Disentangling the Moderating Role of Issue Salience and Party Polarisation

The relevance of public opinion for the survival of the European project reveals the importance of understanding how citizens form their opinion towards the EU. Previous literature suggests that citizens lack information about EU politics and, thus, are very permeable to frames and arguments. I focus on party politicisation of EU issues as a moderator factor of how frames affect public opinion formation. The concept of party politicisation of the EU consists of two main dimensions - salience and polarisation - which, I argue, may influence the effect of frames on public opinion formation on EU issues differently. On the one hand, the salience of EU issues implies that individuals are more likely of knowing and having already a stable opinion of them. On the other hand, the polarisation of EU issues indicates individuals which issues are at the centre of party competition and when motivated reasoning should be activated. To test this argument, I use a factorial experiment that manipulates how citizens react to frames in different contexts of party politicisation of the EU during the campaign for the 2022 Portuguese legislative elections. The results suggest that the effect of frames is highly affected by the salience of the EU issues/policies. When respondents already have some knowledge and an opinion on EU issues, they are less likely to be influenced by the frames they are presented with. Polarisation does not influence the way citizens react to frames. This finding is contrary to the expectation that polarisation enhances motivated reasoning.