Why would a supranational law enforcer suddenly refrain from wielding its powers? The authors theorize the supranational politics of forbearance—the deliberate underenforcement of the law—and explain how they arise from cross-pressures between prosecutorial discretion and intergovernmental policy-making. The article then traces why an exemplary supranational enforcer—the European Commission—became reluctant to launch infringements against European Union member states. While the Commission's policy-making role as engine of integration has been controversial, its prosecutorial role as guardian of the Treaties has been viewed as less contentious. Yet after 2004, infringements launched by the Commission plummeted. The authors demonstrate that the Commission's political leadership grew alarmed that aggressive enforcement was eroding intergovernmental support for its policy agenda. By reining in the bureaucrats managing enforcement and embracing conciliatory dialogues with governments, the Commission sacrificed its role as guardian of the Treaties to safeguard its role as engine of integration. The article's findings highlight the consequences of politicizing international institutions and the tradeoffs facing executives double-hatting as prosecutors and policymakers.