How does a court’s policy-making authority shape the nature of judicial behavior? We argue that judicial systems that limit policy-making authority also discourage the politicization of courts, encouraging judges to think narrowly about the interests of litigating parties. In contrast, granting a court high policy-making authority—affecting potentially thousands of cases and other branches of government—naturally encourages judges to consider broader ideological principles. Typically, unraveling cause and effect would be difficult, as judicial behavior and institutions are usually stable and endogenous. But an especially stark sequence of political and institutional changes in Brazil affords analytic leverage to explore these questions. A series of judicial reforms greatly expanded the Brazilian Supreme Court’s authority, and our analysis of judicial decisions shows the emergence of a political cleavage on the court after these reforms.