The Affordable Care Act is a landmark piece of social legislation with the potential to reshape health care in the United States. Its potential to reshape politics is also considerable, but existing scholarship suggests conflicting expectations about the law's policy feedbacks, especially given uneven state-level implementation. In this article I focus on the policy feedbacks of the law's Medicaid expansion on political participation, using district-level elections data for 2012 and 2014 US House races and cross-sectional survey data from 2014. I find that the increases in Medicaid enrollment associated with the expansion are related to considerably higher voter turnout and that this effect was likely due to both an increase in turnout for new beneficiaries and a backlash effect among conservative voters opposed to the law and its implementation. These results have important implications for our understanding of the ACA and of the impact of welfare state expansions on political participation, particularly in federalized systems.