About 6 in 10 Democrats at the Iowa caucuses on Monday reported that they support eliminating private health insurance as part of establishing a single-payer health-care system, according to preliminary poll results, suggesting that most of the party’s voters agree with Sen. Bernie Sanders (I-Vt.) on the divisive issue.

Sanders has campaigned on a Medicare-for-all health-care system in which every American would be placed with a single government insurer, regardless of whether they want it or not.

Critics, including numerous moderate Democrats, have said the single-payer plan could prove politically toxic by forcing the more than 150 million Americans who receive their insurance through their employers to switch to the government plan.

Medicare-for-all supporters say their plan would give Americans security by guaranteeing that they have a government health plan, even if they get fired or lose their job.

The debate has proved to be a defining fissure throughout the Democratic presidential campaign and led to repeated clashes at the debates, with the moderate presidential candidates accusing Sanders of adopting a dangerously unpopular position.

Several Democratic presidential candidates backed Medicare-for-all at the outset of the race but eventually backed off amid heavy criticism and polling suggesting people like the private insurance they have.

The preliminary exit polls, conducted by Edison Research, found that 57 percent of Iowa Democratic caucus-goers support a single-payer plan, and 38 percent oppose the proposal to eliminate private health insurance, leading some single-payer supporters to claim they were vindicated.

“The conservative wing of the Democratic Party has been telling us voters won’t swallow Medicare-for-all once they learn they will lose their insurance,” said Matt Bruenig, founder of People’s Policy Project, a socialist think tank. “But these results show voters are ready for Medicare-for-all. What more is there to say?”

About 4 in 10 Democrats also said health care was the most important issue for them, making it the leading issue, followed by climate change. Health care also rates consistently as a top issue for voters in a general election.

Sanders led among supporters of single-payer health care, with about one-third of this group saying he was their first choice. Sen. Elizabeth Warren (D-Mass.) was in second position, with about one-quarter of their support.

Three years ago, several top Democratic lawmakers threw their support behind Sanders’s single-payer proposal. Sens. Kirsten Gillibrand (D-N.Y.), Cory Booker (D-N.J.) and Kamala D. Harris (D-Calif.), who all ran for president, appeared at a news conference backing Sanders’s legislation.

One by one, however, each of the Democratic senators who had co-sponsored the Medicare-for-all legislation distanced themselves from its least-popular provisions, such as the elimination of private health insurance. Harris, who faced accusations that she flip-flopped on the issue, has dropped out of the race, as have Booker and Gillibrand.

Warren initially aligned herself more closely with Sanders, saying “I’m with Bernie” when pressed on eliminating private health insurance.

Later, she released a plan that would first create an optional government public option and not advance a single-payer system for three years. That alleviated criticisms from centrists who said she wanted to move too aggressively, but garnered new attacks claiming she had waffled on the issue.

For conservatives, the move away from Sanders’s position remains a smart one regardless of the results from Iowa. A Washington Post-ABC News poll this summer found support for single-payer drops significantly, to less than half of Americans, when respondents were told that it would mean eliminating private insurance.

Another poll of Iowa voters by CBS News/YouGov last summer found that two-thirds of Democrats said they preferred a government health program that competed with private insurance instead of getting rid of it outright. Polling among all Americans has found that an optional government public option would be more popular than a single-payer plan.

“There is always a danger in listening to one half of one party when trying to win a general election. The lessons of 30 years of health-care reform are that incrementalism is really the only path,” said Brian Riedl, an economic policy expert at the Manhattan Institute, a right-leaning think tank.

A big chunk of the Democratic Party appeared to agree. Among those who opposed single-payer, former vice president Joe Biden and former South Bend, Ind., mayor Pete Buttigieg led, with each garnering support from about 3 in 10 among this group. Sanders and Warren received support from fewer than 1 in 10 in this group.

Opponents have also argued that single-payer would require prohibitive tax increases, with some think tanks finding that the government would have to raise an additional $30 trillion in revenue over 10 years to pay for the program.

Sanders’s plan proposes moving every American in the country to a single government-run insurer that charges no deductibles or premiums. Doing so would significantly increase government expenditures, while offering health insurance to Americans who lack it and preventing millions more from being forced into medical bankruptcy.

Sanders has said that his plan would be paid for in part with higher middle-class taxes but has said any tax increases would be offset by savings on insurance premiums, deductibles and out-of-pocket costs.