Democrats were naturally declared the big winners of last month’s King v. Burwell Supreme Court decision. That ruling, after all, saved the party’s most significant legislative accomplishment in decades: The Affordable Care Act (ACA).

But Obamacare has not simply been an ideological victory for the Democratic Party. The percentage of Democrats with health insurance has increased dramatically since the ACA’s marketplace went online in October 2013, according to weekly surveys conducted by YouGov for the Economist. In fact, the display below suggests that Democrats’ uninsured rates have essentially been cut in half under Obamacare.


The Republican Party’s uninsured ranks, by contrast, have been much steadier over the past two years. The figure above even indicates that Democrats are now slightly more likely than Republicans to be insured after long trailing behind the GOP in health insurance coverage by wide margins.

Those results are not too surprising. Daily surveys conducted by Gallup-Healthways show that plummeting uninsured rates under Obamacare are especially pronounced among African Americans, Latinos, lower-income individuals, and residents of states that have expanded Medicaid coverage—all of whom at least lean towards the Democratic Party.

The more interesting question is whether Democrats’ stronger support for the ACA has led them to sign up for health insurance at faster rates than Republicans who remain overwhelmingly opposed to Obamacare. While establishing the causal influence of partisanship on health insurance coverage is difficult, there are strong reasons to believe that Americans’ partisan attachments have played an important part in their Obamacare enrollments.

For starters, party identification was a powerful determinant of whether uninsured Americans planned to purchase health care insurance or pay the ACA’s fine down the road for failing to do so.  According to Gallup surveys of nearly 4,000 uninsured adults in the last quarter of 2013, Republicans were three times more likely than Democrats to say they would remain uninsured and pay the fine (45 percent to 15 percent respectively).

Second, I examined data from the Cooperative Congressional Election Study (CCES) and the Kaiser Foundation’s monthly Health Tracking Surveys, which together asked over 200,000 respondents if they had health insurance between 2010 and 2014. After controlling for several demographic factors in those two large surveys—e.g., age, race, ethnicity, gender, income, marital status, education, and state of residence—Democrats’ uninsured rates still fell significantly faster than Republican rates did after Obamacare took effect.

Democrats are also more likely than Republicans to buy their own insurance from health care exchanges created by the ACA–so much so that partisanship was the strongest predictor of purchasing health insurance from a state or federal exchange in the 2014 CCES survey. Even after controlling for the aforementioned demographics, the figure below shows that strong Democrats were twice as likely as strong Republicans to buy their insurance from a health care exchange.


Graph by Michael Tesler. Source: 2014 CCES

Finally, and perhaps most important, party identification was a highly significant predictor of individual-level changes in health insurance status from 2012 to 2014. The final figure below graphically displays those results from the 2012-2014 CCES Panel Study—a survey that re-interviewed over 900 individuals in 2014 who did not have health insurance when they were surveyed back in 2012. That display shows that strong Democrats who did not have health insurance in 2012 were nearly 20 percentage points more likely to be insured in 2014 than their strong Republican counterparts (after controlling for several demographic factors).


Graph by Michael Tesler. Source: 2010-2012-2014 CCES Panel Study

Taken together, the results suggest that Republican opposition to the ACA has spilled over into enrolling for Obamacare. Uninsured Republicans may, therefore, increasingly find themselves torn between their own needs for health insurance and their strong aversion towards the ACA. Indeed, that conflict has recently played out in a number of high-profile incidents in which uninsured opponents of Obamacare now desperately require its assistance.