Since the enactment of the Affordable Care Act (ACA) in 2010, conservatives have sought to undermine the law's entrenchment. While they have failed in their ambitious quest to repeal the ACA, opponents have succeeded in overturning one major provision (the individual mandate penalty), narrowing the law's reach, complicating its implementation, and fomenting doubts about its political sustainability. This essay places the postenactment battle over the ACA in historical-institutional perspective by juxtaposing the strategic choices that conservatives have made to limit the role of the federal government in the core social welfare areas of pensions and health since the New Deal. Our central argument is that conservatives' varying strategies of postenactment opposition, resistance, and accommodation for Social Security, Medicare, Medicaid, and the ACA have been shaped by shifts in conservative ideology, changes in control of institutional resources, and the nature of policy feedback. Attention to these contextual factors helps explain why ACA opponents viewed the law as a threat despite its moderate policy design, why opposition did not subside after the law's enactment, and how conservatives managed to keep the conflict going across multiple election cycles.