Medicare for All is a nice catchphrase, but for a party seeking to unseat President Trump, it is a poison pill that the Democratic candidates should not swallow whole.

The popularizer of the idea, Bernie Sanders, conceded under questioning on the debate stage that the middle class would pay more in taxes, but said that any tax rises would be offset by savings on insurance premiums and deductibles.

Asked for a show of hands which Democrats support Medicare for All, Elizabeth Warren led the charge to declare, “I’m with Bernie.” New York Mayor Bill De Blasio joined her. On the second night, Kamala Harris raised her hand to back Sanders, then following the debate thought better of it, saying she misunderstood the question.

It was the second time Harris walked back her support, even though she is one of four senators running for president who have signed on to Sanders’ Medicare for All legislation. The others are Kirsten Gillibrand, Cory Booker, and of course Warren, who leaned into the issue more than she has in the past, perhaps hoping to poach some of Sanders’ support.

Sanders has made Medicare for All a litmus test for the candidates, says Robert Blendon, a health care expert and professor of politics at Harvard’s School of Public Health. “The political issue is the composition in the Democratic primary, a younger crowd than we’ve seen in decades,” he told The Daily Beast, and they’re driving the conversation.

The broader electorate is hyper-focused on their own health care needs, the cost of prescription drugs, doctor access, unexplained medical bills. “But if you’re one of 20 Democrats in the primary,” Blendon notes, “you’re thinking about activists in Iowa, New Hampshire and California, and activists want some version of Medicare for All.”

The most contentious part of Medicare for All is that in its purest form it would end all private insurance. “Not ideal to run on in the suburbs,” says Blendon, where expensive supplemental insurance is part of the lifestyle, like Starbucks and Whole Foods. Seniors buy add-on plans to Medicare with dental care and fitness classes. “I don’t think most of the candidates thought this through, that they would be telling seniors who retired on Medicare that they would lose the plan they bought through Medicare,” says Blendon.

President Obama got a taste of this when he promised after the passage of Obamacare in 2013, “If you like your health plan, you can keep it.” A couple million people couldn’t, and Politifact made it “lie of the year.”

Taking away something that millions of people like is never a good idea. With health care the top issue for voters, “Talking about Medicare for All hands the Republicans an ICBM, a nuclear warhead they can fire in different directions,” says Matt Bennett, a co-founder of Third Way, a moderate Democratic group. There’s the cost, $32 trillion over 10 years, according to the left-leaning Urban Institute. The payroll tax would likely be doubled, and the choice of private insurance ended or severely restricted. Republicans would have a heyday stoking generalized anxiety about an empowered federal government, or worse, when they’re in charge they could cut back the program.

Democrats won back control of the House in 2018 on the strength of voter concerns about health care. Third Way monitored all the ads in the 95 most competitive House races, and in only two races did the Democratic challenger mention Medicare for All. One was in Eastern Nebraska, the other in Schenectady, New York. Both candidates lost in what were winnable races for seats that had been held by Democrats four years earlier.

“It’s not arbitrary, it’s crystal clear that support goes down significantly once people know more about it,” says Bennett. “Even among Democrats, it just craters when you tell people anything.”

“ With the exception of Sanders, whoever wins the nomination will have to find a way to preserve private insurance or risk a debacle at the ballot box. ”

A Third Way poll last month found that among all Democratic primary voters, support for Medicare for All drops from 65 percent to as low as 23 percent when respondents learn the details. But Third Way also found that among primary voters, “hyper-engaged, daily tweeting Democrats dismiss concerns about Medicare for All. Seven in 10 still support it after hearing it eliminates private insurance, and support never goes below six in 10—even when picturing the prospect of Republicans having complete control over access to health care for women, immigrants, and LGBT people.”

Health care industry lobbyists are marshaling a new coalition “like a stand-by military,” says Harvard’s Blendon, to preserve their role in the delivery of health care. The advocacy group Public Citizen reports nine times as many lobbyists working on Medicare for All in the first quarter of this year as in 2018, with most deployed to oppose the concept. “It has gone from being a quixotic idea to something that is viewed as a legitimate policy proposal,” says research director Taylor Lincoln.

Even if the Democrats win the White House, passing Medicare for All would require 60 votes in the Senate, a goal that is for now out of reach. “What problem are we trying to solve?” asks Ceci Connolly, president and CEO of the Alliance of Community Health Plans. If it’s coverage, expanding Medicaid in states that haven’t would add 3 million people. If it’s drug pricing, take on the pharmaceutical industry. “Our plans are pretty much held over a barrel by drug companies that set the prices, it’s a black box,” she told The Daily Beast.

Democrats have an activist base that is younger and wants structural change, and they have candidates needing that base to win the nomination. Bernie Sanders says the only role for private insurance in the health care system he envisions would be “cosmetic surgery, you want to get your nose fixed.” With the exception of Sanders, whoever wins the nomination will have to find a way to preserve private insurance or risk a debacle at the ballot box. The only nose in need of fixing will be the Democratic Party’s from the pummeling that awaits.