The rise and spread of anti-pluralist ideas is a major threat to democratic regimes. This study investigates why political parties adopt anti-pluralist positions, drawing on evidence from one of the most notorious cases of uncivil politics, the Weimar Republic. Through a supervised text analysis of a novel corpus of party programmes and election manifestos of all electorally relevant political parties in the Weimar Republic, I map variation in anti-pluralist positions over time and across parties. I also analyse whether the adoption of anti-pluralist positions was related to various party characteristics and context conditions. The results indicate that the adoption of anti-pluralist positions was mainly driven by parties’ ideology and electoral competition from more extremist parties, especially on the political right. Qualitative historical evidence suggests that changes in party leadership was a crucial element in the mechanism linking electoral failure to the adoption of antipluralist positions.