The study of health care politics in the United States has long been preoccupied with failure. During the twentieth century, efforts to enact national health insurance repeatedly ended in defeat. Medicare and Medicaid offered an important exception to the norm, though their passage in 1965 presaged not universal health insurance but, rather, further incremental extensions of government coverage to groups, such as children and pregnant women, that commanded political sympathy. From about 1970 to 2010, American health politics operated according to a predictable script: periodic declarations of crisis and calls for urgent action, followed by debate over myriad reform alternatives, all culminating in inaction or incrementalism. As a result, America's uninsured population and health care expenditures climbed upward. The United States became an international outlier in the inequity, insecurity, and expense of its insurance arrangements.

Political scientists offered an array of explanations for the absence of universal insurance in the United States. Fragmented political institutions limited presidents' power, divided reform proponents while giving opponents numerous opportunities to block change, and made it difficult to pass comprehensive legislation through the congressional gauntlet. Influential stakeholder groups used their resources to preserve the profitable status quo for the health care industry and resist measures that threatened their income. Americans' ambivalence about government and fear of anything labeled socialism made it hard for reformers to attract and sustain public support and helped antireform groups scare the public about the allegedly dire consequences of reform (“socialized medicine”).

The proposals to enact new government insurance programs that overcame these obstacles to become law did so by embracing incrementalism and compromising with stakeholder interests. The price for legislative success was limiting public coverage to select populations, forgoing universal coverage, building on existing arrangements, and avoiding cost containment. As spending consequently rose, so too did the price of paying for universal coverage. And the patchwork insurance nonsystem that the United States did establish—comprising Medicare, Medicaid, employer-sponsored insurance, and more—created yet another barrier to reform. Americans were divided into different programs that developed their own constituencies and stakeholders, thereby generating a politics of inertia among the already insured and hindering efforts to disrupt those arrangements or enact a single national health plan that would eliminate the fragmentation.

Many analysts wondered if the United States could ever circumvent these daunting barriers to pass comprehensive reform. The enactment of the Affordable Care Act (ACA) in 2010 was thus a landmark political and policy achievement. Its passage, which was enabled partly by Democrats securing the only filibuster-proof supermajority in the Senate attained by either party between 1980 and 2020, contravened assumptions about American health care politics and the intransigence of the status quo. Judged against prior programs and the typically narrow boundaries of US health policy, the ACA was deeply ambitious, combining a major expansion of access to health insurance with efforts to contain spending and reform health care payment and delivery (including the promotion of accountable care organizations). It moved the United States closer to the norm that all persons should have access to insurance and vastly expanded the federal government's role in regulating health markets.

During its first decade, the ACA has transformed American health care, creating a more equitable, accessible, and (for some) affordable insurance system. About 20 million Americans have gained health insurance. Insurers can no longer discriminate against persons on the basis of health status and preexisting conditions. The law's Medicaid expansion and subsidies to buy private insurance have enabled millions of Americans with modest means to obtain coverage. Moreover, national health spending has grown at a much more moderate rate than predicted at the ACA's enactment.

For all those successes, the ACA has not been without its shortcomings and disappointments. Thirty million persons in the United States still lack health insurance, and the uninsured population, including children, is now growing again. Americans who do not qualify for large subsidies under the ACA struggle to afford coverage in its insurance marketplaces, and many persons with employer-sponsored health plans face high (and rising) deductibles and copayments. ACA policies that were heralded in 2010 as vital cost containment innovations—including the Independent Payment Advisory Board to restrain Medicare spending and the Cadillac tax on high-cost employer plans—have been discarded by Congress, as have taxes on the health insurance and medical device industries. The individual mandate penalty—widely seen a decade ago as essential to the ACA's viability—has been repealed.

The ACA's first decade has generated plenty of surprises. The law has been much more legally vulnerable than anticipated at enactment, saved in a 2012 case only by the deciding vote of Chief Justice John Roberts. The Supreme Court's stunning decision in that same case to make Medicaid expansion effectively optional for states undermined one of the law's foundations, creating a major coverage gap for low-income persons living in states that rejected expansion. Indeed, the ACA's fate in the courts remains unsettled. In the coming years, either the entire law or large portions of it could be scrapped by the Supreme Court in response to an ongoing legal challenge brought by Republican state attorneys general.

Politically, the ACA has shown both remarkable vulnerability and resilience. In Washington, Republicans' opposition to Obamacare has persisted despite the ACA's achievements, widespread benefits, and health industry support. In 2017, the GOP came within a single vote in the Senate of repealing much of the ACA (Republican Senators John McCain, Lisa Murkowski, and Susan Collins, who cast the votes that stopped repeal, joined Chief Justice Roberts as unlikely saviors of the ACA). Even after that failed effort to overturn the law, the Trump administration has attempted to undermine the ACA through administrative actions. Still the law has survived, and amid Republicans' legislative, legal, and administrative assaults it remains mostly intact to date. Medicaid expansion, insurance subsidies, and consumer insurance protections—the ACA's core benefits—are widely popular and reach tens of millions of Americans, making any effort to repeal the ACA politically treacherous.

What lies ahead for the ACA in its second decade? Its future is highly uncertain, contingent on court decisions, electoral results, and political as well as socioeconomic currents that we cannot discern now. Health politics can move in mysterious ways. After all, a decade that began with the ACA preserving private insurance and expanding Medicaid ended with Republicans attempting to curtail Medicaid eligibility and Democrats proposing Medicare-for-all plans that would displace private insurance. The ACA's enactment was a monumental event; 10 years later, its reverberations continue to reshape US health care policy and politics. The ACA did not end the century-long conflict over health care reform in the United States, but it changed that conflict in ways that will extend far beyond 2020.

The articles in this special issue (which actually spans two issues of JHPPL) reflect on the ACA's first decade, evaluating the law's impacts, performance, and evolution from the perspectives of political science, economics, law, health services research, and public health. Authors explore how the ACA has fared compared to original expectations and analyze lessons from the law's implementation and experiences with Medicaid expansion, health insurance marketplaces, choice, and the courts. They illuminate what the ACA tells us about race, policy feedbacks, waivers, federalism, rulemaking, partisanship, and public opinion in American politics, as well as how the ACA looks from a comparative perspective. They examine the ACA in the context of critical health policy issues, including health disparities, health care cost control, and provider consolidation. And they grapple with the ACA's lessons and implications for contemporary reform debates. Taken together, these articles paint a complex portrait of the ACA, its legacies, the state of health care politics, and the enduring challenges in US health policy.

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