Repetition Does Not Increase Belief in Claims From Distrusted Politicians

Repeating falsehoods is a common political tactic, and a large body of research on the illusory truth effect suggests that such repetition should increase belief in these claims. This repetition effect is generally thought to be a low-level cognitive bias that applies broadly across scenarios and people, making it a powerful force in political persuasion. In contrast, we adopt the theoretical framework of adaptive rationality and argue that repetition should not increase belief in claims if they are made by distrusted sources. We test this prediction in a large (N = 2,484) pre-registered experiment in which American partisans are shown real claims made by Donald Trump and Joe Biden, and a randomly selected subset of claims are repeated. Consistent with our predictions, we find that repetition does not increase belief if the participant distrusts the politician making the claim. By showing that source credibility is a powerful moderator of the illusory truth effect, we demonstrate an important limitation on the power of repetition for inducing belief.