Widespread distrust in politicians is often attributed to the way elites portray politics to citizens: the media, competing candidates, and foreign governments are largely considered responsible for portraying politicians as self-interested actors pursuing personal electoral and economic interests. This article turns to the mass level and considers the active role of citizens in disseminating such information. We build on psychological research on human cooperation, holding that people exhibit an interpersonal transmission bias in favor of information on the self-interested, antisocial behavior of others to maintain group cooperation. We posit that this transmission bias extends to politics, causing citizens to disproportionally disseminate information on self-interested politicians through interpersonal communication and, in turn, contributes to distrust in politicians and policy disapproval. We support these predictions using novel experimental studies allowing us to observe transmission rates and opinion effects in actual communication chains. The findings have implications for understanding and accommodating political distrust.