The Affordable Care Act (ACA) was enacted in a deeply polarized context, and it has endured multiple challenges to its implementation and its very existence that continue to this day. Yet, we find that the law is entering a new phase of acceptance among the American public, such that it presents political risks to politicians who would dare to weaken it. We have conducted a panel study of Americans' public opinion on the ACA since 2010, returning to the same respondents every two years to ask the same questions. This approach, which is essential for tracking change, reveals that support for the ACA is growing and the most intense opposition is receding. It also shows that Americans' sense of the law's impact on their lives is at least holding steady and in some respects growing. Most strikingly, those who feel favorably toward the law are more engaged politically than those who oppose it, and they are more likely to take it into account when they vote. These trends indicate that the law, despite the legal and political obstacles it still confronts, is becoming more firmly established in public opinion and through patterns of political participation.