A large body of scholarship in political science has examined the extent to which the Supreme Court is constrained by congressional preferences when it decides cases. It remains unresolved, however, the extent to which political checks and balances constrain the Court and the conditions under which those constraints are most efficacious. This dissertation combines formal modeling with elite interviews to develop a theory of Court-Congress relations. I argue proposed legislation in Congress serves as a signal to the Court about its institutional legitimacy and can help explain the conditions under which the Supreme Court should appear to be a constrained decision-maker. Building on evidence from interviews with Supreme Court justices, members of Congress, former law clerks, and legislative staffers, I argue the Supreme Court will exercise self-restraint when it is concerned about losing institutional legitimacy. I develop a formal model of legislative-congressional relations that generates empirical hypotheses about the nature of the relationship between congressional hostility and judicial decision-making. In the model, a strategic Congress communicates information to the Court about public support for the Court and simultaneously leads public opinion about the Court. The dissertation posits that, rather than responding to congressional preferences directly, the Supreme Court will be most likely to exercise self-restraint when institutional signals reveal waning judicial legitimacy.

To assess the theoretical predictions, I assemble an original dataset including all Court-curbing proposals introduced in Congress between 1877 and 2006. Court-curbing bills are pieces of legislation seeking to restrict or remove judicial power. The introduction of Court-curbing is first treated as a dependent variable, using data on public opinion, Supreme Court decisions, and theories of congressional behavior to assess the theoretical model's predictions about when Congress should engage in legislative attacks on the Court. Next, Court-curbing is used as an independent variable to explain variation in the Court's decision-making. The analyses show the Supreme Court exercises self-restraint when members of Congress send institutional signals that can credibly communicate public discontent with the Court. Evidence from the statistical analyses is combined with evidence from archival research to provide a reinterpretation of several historical examples of Court-Congress conflict.