Recent studies provide evidence that income inequality is a relevant driver for the electoral success of populist parties all over Europe. In this article, we aim to understand how exactly increasing income inequality can lead to support for populist parties. More specifically, we discuss four different attitudinal mechanisms from previous research: economic insecurities, trust in political elites, social integration, and national identity. We rely on eight waves of the European Social Survey and find that economic insecurities, trust in political elites, and national identity are linked to rising income inequality and populist support as expected. However, a causal mediation analysis shows that these mechanisms are not sufficient to fully understand the impact of income inequality on support for populists. This finding raises questions regarding the empirical support of existing theories to explain how macroeconomic changes in inequality became a pre-condition for the rise of populist parties.