Republicans are in a bind. They’ve been promising to repeal Obamacare for seven years, and having won control of the White House and Congress, they had to try to deliver. But while their bitter denunciations of the Affordable Care Act may have depressed its approval numbers, they didn’t make replacing it any easier.

On the contrary, the repeal-and-replace bill designed by House Speaker Paul D. Ryan drew withering criticism from the left and the right. Liberals condemned its use of reductions in health coverage for the poor to pay for large tax cuts for the wealthy, while conservatives bemoaned its retention of many subsidies adopted under Obamacare.

In the end, the repeal effort’s biggest hurdle may have been loss aversion, one of the most robust findings in behavioral science. As numerous studies have shown, the pain of losing something you already have is much greater than the pleasure of having gained it in the first place. And the nonpartisan Congressional Budget Office estimated that Mr. Ryan’s American Health Care Act (A.H.C.A.) would have caused more than 14 million people to lose coverage in the first year alone, with total losses rising to 24 million over the next decade. Many Republicans in Congress were nervous about the political firestorm already provoked by the mere prospect of such losses.

Loss aversion actually threatened the repeal effort on two fronts: voters’ fear of losing their coverage, and lawmakers’ fear of losing their seats. Like the first fear, the second appeared well grounded. Republican voters wouldn’t have been the only ones losing coverage, of course, but early studies suggested that losses would have been concentrated among people who voted for President Trump. The Congressional Budget Office estimated, for example, that the A.H.C.A. would have caused premiums to rise more than sevenfold in 2026 for 64-year-olds making $26,500.