J. Lasser, S. Aroyehun, Fabio Carrella
The spread of online misinformation is increasingly perceived as a major problem for societal cohesion and democracy [1, 2]. Much attention has focused on the role of social media as a vector of misinformation . The role of political leaders has attracted less research attention, even though leaders demonstrably inﬂuence media coverage  and public opinion , and even though politicians who “speak their mind” are perceived by segments of the public as authentic and honest even if their statements are unsupported by evidence or facts [6–8]. Here we show that in the last decade, politicians’ concept of truth has undergone a distinct shift, with authentic but evidence-free belief-speaking becoming more prominent and more diﬀerentiated from evidence-based truth seeking. We analyze communications by members of the U.S. Congress on Twitter between 2011 and 2022 and show that political speech has fractured into two distinct components related to belief-speaking and evidence-based truth-seeking, respectively, and that belief-speaking is related to spreading of untrustworthy information. We show that in tweets by conservative members of Congress, an increase in belief-speaking of 10% is associated with a decrease of 6.8 points of quality (using the NewsGuard scoring system) in the sources shared in a tweet. In addition, we ﬁnd that an increase of belief-speaking language by 10% in the shared articles themselves is associated with a drop in NewsGuard score of 4.3 points for members of both parties. By contrast, increase in truth-seeking language is associated with a slight increase in quality of sources. The results support the hypothesis that the current ﬂood of misinformation in political discourse is in part driven by a new understanding of truth and honesty that has replaced reliance on evidence with the invocation of subjective belief.