The Rise and Fall (and Rise) of the Affordable Care Act : Varying Impacts on Coverage Over Time and Place

The Affordable Care Act (ACA) significantly expanded health insurance in the United States, but its impact has varied across time and states. We assess the law's heterogeneous impacts over the three presidential administrations since its enactment, as well as across states with different levels of implementation of the law. We focus on Medicaid expansion and Marketplace subsidies, including the enhanced subsidies under the American Rescue Plan of 2021 (ARP). We use national household survey data and a triple-difference design - leveraging variation by time, state, and income - to identify the coverage impacts of the key components of the law. We find that 55% of ACA-related coverage gains between 2013 and 2023 came from Marketplace subsidies - about 37% from the original ACA subsidies and 19% from the ARP enhancements - while 45% were due to Medicaid, including from the "welcome mat" effect. Coverage gains differed substantially across presidential administrations, with Marketplace subsidies proving roughly 30% more effective under Presidents Obama and Biden than under President Trump. The same subsidy amount was more than twice as effective in states with their own Marketplaces than in states relying on the federal Marketplace. Our findings highlight that while the ACA's explicit economic features drive coverage gains, their effectiveness can be substantially enhanced or hindered through federal and state implementation