After decades of failed efforts to overhaul American health care, the Affordable Care Act's 2010 enactment was the most important health reform achievement since Medicare and Medicaid's passage. But ten years later, ACA politics are more tenuous than triumphal, and the ACA has not escaped the controversy that surrounded its enactment. This article explores why the ACA has been so divisive despite its considerable accomplishments. The ACA contains an array of controversial policies that contravene policy principles and political priorities held by the contemporary Republican party. It also imposes costs on stakeholder groups whose opposition, in many cases, to measures that altered the status quo has never ceased. Moreover, ACA benefits often have been obscured, partly because of the law's complex structure and incoherent programmatic identity. Additionally, the ACA's performance on its central promise-to make health insurance affordable-has been mixed. The law also confers benefits on populations that command less political sympathy than those previously favored with public coverage, and it has surfaced perennial racial/ethnic tensions related to who receives government benefits. I argue that the ACA's turbulent political journey ultimately reflects the larger trends in American politics of growing partisanship and polarization that continue to shape US health policy.