Disinformation emphasizing radical populist narratives may threaten democratic values. Although extant literature has pointed to a strong affinity between disinformation and the populist radical right, we know little about the effects of such deceptive information. Against this backdrop, this article relies on an experiment in the Netherlands (N = 456) in which participants were exposed to radical right-wing populist disinformation versus decontextualized malinformation. Mimicking the participatory logic of disinformation campaigns in the digital society, we also varied the source of the message (a neutral news message versus a social media post of an ordinary citizen). Main findings indicate that exposure to radical right-wing populist messages can prime support for radical-right-wing issue positions, but ordinary citizen sources do not amplify disinformation’s effects. Our findings indicate that malign populist messages may have a delegitimizing impact on democracy, irrespective of how they are presented.