The Affordable Care Act of 2010 (ACA) is a landmark in American social policy that is disrupting America’s “liberal tradition.” It is successfully expanding access and compelling insurers to change their business models to serve more socially-useful purposes, cost control enjoyed initial success but confronts barriers rooted in America’s resilient political economy. The ACA is disrupting long-standing patterns of American politics, introducing new developmental paths that unsettle or, in certain respects, offset the familiar patterns of selectivity, deference to private markets, and “drift” that tend to produce government inaction as economic insecurity increases. New policy arrangements for financing and delivering medical care is ushering in a new politics of US health care that are resetting the terms of future debate, the ACA is also challenging familiar approaches to studying politics including analyses of framing, policy effects and political development, and American political thought.