When and how can institutions lead public opinion? Scholarly controversy exists over whether even a highly esteemed institution such as the Supreme Court can move mass opinion. In this study we use an experimental design embedded within a representative national survey to examine these questions in a context involving multiple institutions and multiple issues. Our findings suggest that the Court’s ability to move opinion is potent and based on multiple processes of persuasive influence. Congress’s ability to move opinion, while conditional, is surprisingly more potent than previously understood. Moreover, opinion change in response to institutional endorsements is mediated by substantive political thought to a greater extent than heuristic explanations have suggested.