This paper deduces conditions under which populism successfully emerges in democratic contexts. Building on Downs’s economic theory of democracy, it hinges on three assumptions: uncertainty, rationality, and democratic stability. This theory considers three main types of agents: citizens, political parties, and information providers. We demonstrate that the necessary and sufficient conditions for a populist party to emerge and gain significant electoral support are 1) a political disequilibrium between demand (citizens’ preferences) and supply (parties’ platforms) combined with 2) democratic instability due to ideological polarization. Such conditions provide the rationale behind populist anti-elitism and its thin nature as an ideology. Since this paper provides a theoretical account of populism that, while sharing Downsian roots, differs from main political economy models of populism, we provide a systematic comparison. In particular, we show that the conditions under which the Median Voter Theorem is relevant are at odds with the conditions required to account for populism.
