How does the diffusion of populist rhetoric among populist and non-populist politicians affect public support for multilateral and bilateral foreign aid? Extant research shows that populist elite communications can reduce public support for international solidarity and trust in international organisations. However, framing effects are generally moderated by citizens’ evaluation of the “source” of the message. Indeed, recent work suggests that the effect of populist party cues remains limited to citizens who already hold favourable views of populists (Bayram & Thomson 2022). However, in response to the electoral gains of populist parties, mainstream parties increasingly adopt populist frames and populist policy positions, leading to a “mainstreaming” of populist discourse. We argue that the use of populist frames by mainstream parties affects also citizens who are usually not responsive to cues from populist parties. In particular, we theorise that individuals who support mainstream parties or do not hold populist attitudes are less likely to respond to cues from populist parties but might be affected by populist frames, if they are voiced by mainstream political actors. Thus, populist discourse may undermine broader public support for multilateral international solidarity. We test this argument in the area of international health policy using a novel vignette experiment embedded in a cross-national public opinion survey which will be fielded in January 2025. Specifically, our experiment varies both the message – a negative or positive framing of multilateral medical aid – and the source – a populist or a mainstream party. Our study contributes to research on the effect of populism on public support for international solidarity and, in particular, to the effect of the diffusion and “normalisation” of populist discourse among mainstream parties. Finally, by investigating the relative importance of frames and party cues in the area of international solidarity, our study contributes to the long-standing debate whether the message or the messenger matters more in shaping citizens’ opinion.
