Misplaced Certainty in U.S. Presidential Rhetoric Predicts Political Violence

Can false claims by political leaders be brushed aside as harmless, or does such rhetoric carry serious consequences? By applying large language models to U.S. Presidential speeches spanning 1850 to 2024, we find that presidential assertions of falsehoods as fact—which we term misplaced certainty—are associated with a subsequent rise in politically violent events. Underscoring the relevance of these findings, we identify a comparative shift toward such rhetoric in Republican versus Democratic presidents beginning around 1980, with Donald Trump exhibiting particularly extreme values. Providing experimental support, we find individuals’ support for political violence to increase after exposure to excerpts high in misplaced certainty from the 2024 Harris-Trump presidential debate. Our findings highlight the dangers of political leaders expressing unwarranted certainty in false claims.