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 (between 2013 and 2023), as well as across states with different levels of implementation of the law. We focus on the law's 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, place, and income-to identify the coverage impacts of the key components of the law. We find that about 50% of ACA-related coverage gains between 2013 and 2023 came from Marketplace subsidies-about 40% from the original ACA subsidies and 10% from the ARP enhancements-while the remaining half were due to Medicaid, including from the "welcome mat" effect. Coverage gains differed substantially across presidential administrations, with Marketplace subsidies in particular proving more effective under Presidents Obama and Biden than under President Trump. The same subsidy amount was >1.5 times as effective in states running their own state-based Marketplaces than in states relying on the federal Marketplace, and this result persists even after accounting for states' political ideology. 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.