The U.S. Supreme Court is traditionally thought to hold little influence over social or political change; however, recent evidence suggests the Court may wield significant power, especially with regard to criminal justice. Most studies evaluate judicial power by examining the effects of individual rulings on the implementation of specific policies, but this approach may overlook the broader impact of courts on society. Instead, I adopt an aggregate approach to test U.S. Supreme Court power. I find that aggregate conservative decision making by the Court is positively associated with long-term shifts in new admissions to U.S. federal prisons. These results suggest the Court possesses significant power to influence important social outcomes, at least in the context of the criminal justice system.