Medicare for all, which Bernie Sanders and Elizabeth Warren have championed on the campaign trail, would offer all Americans generous government-run insurance, while sharply reducing pay to doctors, hospitals and pharmaceutical companies. Plans from other candidates, including Joe Biden and Pete Buttigieg, would set up a “public option,” a government health plan that individuals could buy. That plan would also pay doctors and hospitals less than they earn now.

Both Democratic approaches poll fairly well. But a policy to end surprise medical billing, a smaller endeavor, polls even better, and it has emerged as a top voter concern. In a recent survey from the Kaiser Family Foundation, 78 percent of adults said they wanted the surprise billing problem fixed, and 57 percent said they would still support a solution even if it meant lower pay for health care providers.

Health care providers, of course, do not want their pay to be lowered.

When the legislative process heated up this summer, so did a fierce lobbying effort from doctors and hospitals. Doctor Patient Unity, a dark money group funded by two large private- equity-funded physician staffing companies, spent tens of millions on television advertisements and direct mail, urging lawmakers to oppose the bill. Lobbyists for doctors, hospitals, air ambulance companies and private equity funds also began making the rounds. Doctors have argued for a different solution to the surprise billing problem that would not cut their pay.

Research has shown that a small minority of doctors send surprise bills, and they are clustered in a handful of specialties where patients cannot choose their own doctor, including emergency medicine and anesthesiology. But the ability to send surprise bills affects the negotiating dynamics between that subset of doctors and insurance companies.

The surprise billing legislation in the recent deal would set a default payment to doctors for situations in which they were not in an insurance network, with the ability to appeal larger bills to an independent arbitrator. According to the Congressional Budget Office, the approach would tend to lower pay for doctors in those specialties by an average of 15 percent to 20 percent, because it would shift negotiating leverage in favor of insurers.