Past research has devoted more attention to the consequences of populism for party politics and democratic governance than to its effects on public attitudes—and particularly, how populist claims interact with nationalism to exacerbate exclusionary beliefs among the public. Using online survey experiments, we examine whether exposure to populism increases out-group antipathy among Democrats and Republicans. In Study 1, we randomly assign respondents to three conditions featuring vignettes based on political speeches: a morally neutral argument, a populist critique of political elites and a morally framed anti-immigration appeal. The results demonstrate that the populist treatment generates lower feeling-thermometer ratings of minority groups than the control condition, but only among Republicans and Trump supporters. Study 2 uses a similar design to evaluate the link between left-wing economic populism and economic nationalism: the populist condition features a critique of economic elites, the nationalist condition blames China for the offshoring of US jobs and the outcome variable measures respondents’ sentiments toward China. Economic nationalism generates increased anti-China sentiment among moderate and conservative Democrats but economic populism does not. Together, these findings suggest that the effects of populism on nationalist antipathies observed in Study 1 are driven by the discursive bundling of anti-elite talk with ethno-nationalism on the political right, which stands in contrast to the decoupling of economic populism from economic nationalism on the left. The former has effectively turned populism into a form of dog-whistle politics among Republicans, and Trump supporters in particular.