Policy Effects, Partisanship, and Elections: How Medicaid Expansion Affected Public Opinion toward the Affordable Care Act

The Affordable Care Act (ACA) is one of the most consequential policies enacted in recent decades, but its political divisiveness and complexity call into question whether its effects can change public opinion. Using the varied implementation of one of the ACA’s key provisions—the expansion of Medicaid—and nearly 300,000 survey responses analyzed using a difference-in-differences design, we find the expansion of Medicaid makes respondents 1.5 percentage points more positive toward the ACA and 2.2 points less likely to support repealing the ACA. Effects do not vary meaningfully by partisanship, are strongest for those most likely to be directly affected, and are stronger after the 2016 election increased the chances of repeal. In addition to highlighting the ability of partisan policies to change public opinion when credibly threatened, we demonstrate how to estimate changes in model-based group opinion without bias.