A big fight has opened up in the Democratic presidential race. It’s between “Medicare for All”—a single-payer system that would abolish and replace private health insurance—and a “public option,” which would offer a Medicare-style alternative to private insurance plans but wouldn’t abolish them. This fight could well decide the nomination. Health care is a huge voting issue: It’s universal, it has enormous personal financial consequences, and for many, it’s a matter of life or death.

Two candidates near the front of the pack, Sen. Elizabeth Warren and Sen. Bernie Sanders, are defending Medicare for All. The rest of the field, by and large, is defending some kind of public option. Judging by Thursday night’s debate in Houston, Warren and Sanders are in trouble.

Part of the fight is about money. Sanders and Warren say their Medicare for All bill will get rid of premiums, copays, and deductibles, which people hate. Former Vice President Joe Biden, the leading proponent of a public option, points out that the Sanders-Warren bill would instead fund health care by raising taxes, which people hate. Some voters will end up choosing sides based on who would be taxed and how much. That’s a messy question, since each camp uses projections that suit its agenda.

Polls on this issue are complicated. Among voters as a whole, a public option is more popular than Medicare for All. Among Democrats, it’s a closer call. People like the security of a single-payer system that’s always there for them. But they don’t like being coerced. And many Americans who have good employer-provided health plans don’t want to give them up for Medicare coverage that in some cases is less generous.

People like the security of a single-payer system that’s always there for them. But they don’t like being coerced.

In Thursday’s debate, Biden and other candidates raised these criticisms against Warren and Sanders. Beto O’Rourke, the former Texas congressman, objected to “forcing tens of millions off of insurance that they like, that works for them, to force them onto Medicare.” Pete Buttigieg, the mayor of South Bend, Indiana, told Sanders, “I trust the American people to make the right choice for them. Why don’t you?” California Sen. Kamala Harris, Minnesota Sen. Amy Klobuchar, and former Housing and Urban Development Secretary Julián Castro agreed that people shouldn’t be forced into a government plan.

Warren and Sanders offered several rejoinders. To begin with, they argued, people who like their current health care are more attached to their doctors than to their insurers. “I’ve actually never met anybody who likes their health insurance company,” said Warren. “I’ve met people who like their doctors. I’ve met people who like their nurses.” Under Medicare for All, she asserted, they could keep all of that. The only difference, she said, was “where to send the bill.”

Second, Warren pointed out that private insurers already restrict people’s choices. They don’t cover—or, in many cases, inadequately cover—some doctors and procedures. “Sorry, you can’t see that specialist,” Warren chirped, mocking what insurance companies tell policyholders. “Sorry, that doctor is out of network. Sorry, we are not covering that prescription.” The whole business model of private insurers, she protested, is “saying no to coverage.”

Third, as to people’s fears of losing their private insurance policies to a government takeover, Sanders observed that those policies are lost under the status quo anyway, due to changes in the job market. “Fifty million … people lose their private insurance every year when they quit their jobs, or they go unemployed, or their employer changes their insurance policy,” Sanders reminded his critics.

Unlike these tenuous private plans, said the two senators, Medicare for All would cover all physicians. “It allows you to go to any doctor you want, which many private insurance company programs do not,” said Sanders. Warren offered the same assurance: “People will have access to all of their doctors, all of their nurses, their community hospitals, their rural hospitals.” The bottom line, said Sanders, was greater “freedom of choice.”

These arguments resonate with many people’s bitter experiences of private health insurance, and they puncture the dogma that everyone is freer when the government defers to markets. But they don’t settle the debate. The rebuttals on behalf of a public option are stronger than the arguments for a single-payer system, even in a Democratic primary.

First, the public option is safer. It’s a less radical change. It upsets fewer stakeholders—unions, for example, can keep high-quality private plans if they’ve already bargained for them—and it poses fewer risks. “I go with the doctor’s creed, which is, ‘Do no harm,’ ” Klobuchar explained during the debate. Under Sanders’ Medicare for All bill, she noted, “149 million Americans will no longer be able to have their current insurance.” Sanders replied that under the bill, employers would have to compensate unions for collectively bargained insurance coverage forfeited in a government takeover. But Biden poked fun at that promise, appealing to workers’ skepticism. “For a socialist,” he told Sanders, “you’ve got a lot more confidence in corporate America than I do.”

Second, although many people don’t like their current insurance plans, many others do. In a Gallup poll taken nine months ago, 85 percent of people on private insurance said their health care was good or excellent, 70 percent said their coverage was good or excellent, and 51 percent were satisfied with the cost. By comparison, 70 percent of people on Medicare or Medicaid, as a combined population, were satisfied with the cost of their care. Still, a lot of folks are reluctant to surrender their private plans. Two months ago, in a Marist poll, only 8 percent of Democrats opposed a system that would “allow all Americans to choose between a national health insurance program or their own private health insurance.” But 31 percent opposed “a national health insurance program for all Americans that replaces private health insurance.” Last month, when a Monmouth survey asked Democrats to choose among various health care systems, only 22 percent preferred to “get rid of all private insurance coverage in favor of having everyone on a single public plan like Medicare for All.” Fifty-three percent preferred to “allow people to either opt into Medicare or keep their private coverage.”

Third, Americans don’t like being pushed around, even when you swear it’s good for them. “The problem, Sen. Sanders, with that damn bill that you wrote—and that Sen. Warren backs—is that it doesn’t trust the American people,” Buttigieg told Sanders. Instead, the South Bend mayor proposed “Medicare for all who want it,” a government plan that people could choose to join at any time, instead of paying for private insurance. “I trust you to choose what makes the most sense for you,” Buttigieg told viewers. “Not my way or the highway.”

Fourth, the public option provides the same security as Medicare for All. Suppose, as Sanders warns, you lose your job and the health insurance that came with it. No problem, Biden told the debate audience: Under his system, you can switch to a government-run plan, no questions asked. Or suppose you decide your employer’s plan is too skimpy or expensive. No problem, said O’Rourke: “Everyone who’s insufficiently insured, [or who] cannot afford it, can move over to Medicare.”

Fifth, if Medicare for All turns out to be a better deal than all private insurance, then consumers will vote with their feet. They’ll flock to the public option, and we’ll end up in a single-payer system. But we’ll get there without coercion—and with the benefits of competition and pilot testing. “If we’re right, as progressives, that that public alternative is better,” Buttigieg reasoned, “then the American people will figure that out for themselves.”

One group is already voting with its feet: the candidates. Two and a half months ago, in the first Democratic debates, few of the viable contenders were willing to speak up against Medicare for All. Now they’re gaining confidence that a noncoercive alternative, framed as a public option or as a form of Medicare, is politically safer as well as more practical. Harris, who stood with Warren and Sanders in her first debate, distanced herself from them on Thursday. “Under my Medicare for All plan, people have the choice of a private plan or a public plan, because that’s what people want,” said Harris. “We shouldn’t take choice from people.”

Even Warren, who seldom ducks a fight, is getting cagey about this one. Twice on Thursday, George Stephanopoulos asked her whether, under the bill she’s supporting, “private insurance is going to be eliminated.” Twice, Warren sidestepped the question. That’s not the behavior of a candidate who’s confident that people are happy to abolish private coverage. It’s the behavior of a candidate who’s in doubt.