In mid-November, a few dozen of the country’s most influential advocates of Medicare-for-all were reviewing details of Sen. Elizabeth Warren’s plan to finance the proposed government-run program when they learned that she had unexpectedly changed her position.

Warren (D-Mass.), who had excited liberals when she initially embraced a Medicare-for-all idea first proposed by rival presidential candidate Sen. Bernie Sanders (I-Vt.), was suggesting a more centrist idea: to delay enactment of the single-payer system and, in the interim, give consumers the choice to opt in. The change might have seemed insignificant to most Americans, but to many in the suburban Washington conference room, Warren’s new stance marked an abrupt retreat, according to several people in attendance.

That moment highlighted the political turbulence that Warren has experienced in recent weeks as she has attempted to extricate herself from a policy dilemma that has blunted her steady rise to the top ranks of the Democratic nominating contest.

Twelve Democratic presidential candidates took strong stances on various policy issues during the fourth debate in Columbus, Ohio on Oct. 15. (The Washington Post)

Warren had pleased many on the left with proposals to take on entrenched corporate and political power. But she was being warned that support for Medicare-for-all, including the elimination of private health insurance used by more than 150 million Americans, could cost her support among Democrats looking for the strongest candidate to take on President Trump.

“As [Medicare-for-all] got more attention, more and more people began to say, ‘Yeah, that’s a mistake [that] she showed flexibility,’ ” said former congressman Barney Frank of Massachusetts. “But I guess she felt she couldn’t make herself totally vulnerable to the Sanders people by abandoning [Medicare-for-all] altogether.”

“It would have been better to do it earlier,” Frank said of her shift, adding that he had privately told her that backing the Sanders plan was “a terrible mistake.”

Recent polling suggests Warren has sustained political damage from her health-care policy. After climbing to the top of the field by focusing on a message of overhauling Washington and Wall Street, Warren plateaued as her campaign became consumed with health care.

Now, she is falling.

Nationally, Warren has dropped from a high of about 27 percent in October’s RealClearPolitics’ average of polls to near 16 percent at the end of November. In Iowa, she has dropped about five points in that same period, and in New Hampshire, her support has been cut in half, according to the calculation. Warren’s decline has coincided with the rise of a new entrant into the top tier: South Bend, Ind., Mayor Pete Buttigieg, who has backed a more moderate health-care agenda and accused Warren of failing to make clear how she would pay for her plan.

This account of Warren’s health-care policy struggles — and the political repercussions that have rapidly shifted the dynamics of the 2020 Democratic race — is based on interviews with 27 advisers, experts and others familiar with the campaign’s deliberations on the issue, many of whom spoke on the condition of anonymity to speak candidly.

The irony is that a candidate whose political identity has been built in part on her reputation as a policy wonk — a potential president who boasts of having a plan for nearly every challenge facing everyday Americans — has been tripped up by a policy issue that has dominated politics and defined her party for years.

In some ways, the health-care debate was uniquely suited to entangle Warren, who as a senator had never made the issue a central element of her worldview.

She embraced a single-payer system as she planned her presidential run, signing onto Sanders’s Medicare-for-all bill in 2017. But Warren wanted — and felt duty-bound by her brand — to offer detailed plans to explain how it would work. Then the landscape shifted, as health-care industry groups aired ads attacking her plan and some top-tier rivals said she was refusing to acknowledge what Sanders had conceded: that middle-class taxes would rise to pay for it.

The result for Warren is a muddle, with some liberal activists feeling betrayed and little evidence emerging that she has neutralized criticism from the middle.

“As Warren’s health-care plan has been fleshed out, it does very much straddle the moderate and progressive wings of the Democratic Party right now,” said Larry Levitt, the executive vice president for health policy at the Kaiser Family Foundation. “As is often the case when you’re trying to straddle, you don’t satisfy either side.”

Warren’s team says that she has strongly supported Medicare-for-all since she signed on to Sanders’s bill. She has repeatedly told reporters that she has been working for “months and months” to develop a way to pay for it that doesn’t include higher taxes on the middle class, which some economists say she has achieved.

Several academics noted that they’d been in touch with Warren’s campaign since early in her candidacy about key details. “I’ve been very impressed by the intellectual discipline,” said Donald Berwick, a former Obama administration health-care official who often emailed with the campaign about her proposal.

“I’ve always seen a very pragmatic side to the way she thinks about health policy,” added Ezekiel Emanuel, another top health-care expert who has offered advice to Warren in her roles as senator and presidential candidate. “I think that’s been my major understanding of who she is as a person and how she thinks about things. . . . That’s the way I heard the recognition of the revised timeline.”

Some of Warren’s allies are privately frustrated by what they see as the gaps that Sanders left unfilled in his health-care plan and his willingness to “self-immolate,” as one person said, his chances in a general election by supporting a hike to middle-class taxes to pay for it.

So far, Warren’s pivot on her approach to Medicare-for-all hasn’t fully reassured some leading Democrats who are drawn to her but not yet sold.

“She would have sealed the deal if she said, ‘Make no mistake, I think Medicare-for-all is the right thing and I’m going to create a structure to study it and finance it. But in the meantime, I’m going to provide a guide path,’ ” said one top New Hampshire Democrat.

Meanwhile, the pivot to calling for a transition phase opens questions about what Warren believes. “It looks defensive,” this person said.

The origins of Warren’s health-care conundrum can be traced to her earliest days in politics.

She didn’t support single-payer health care in her 2012 Senate run. And as a new senator,Warren was never seen as an ally in the fight for government-run health care, even by the liberal groups who otherwise supported her.

“It’s this weird relationship where everyone really respects her, but it didn’t feel like we had someone out in front as a health-care justice warrior,” said Ture Turnbull, who served as executive director of MassCare, a Massachusetts health-care advocacy group. Turnbull added that Warren seemed mostly focused on protecting the Affordable Care Act.

Though she had signed onto Sanders’s bill, Warren rarely mentioned the program on the stump in the opening weeks of her presidential campaign this year.

She appeared to keep her distance in high-profile interviews, telling Bloomberg TV in January that there are “multiple bills” that ensure affordable health care for every American. In March, she said in a CNN town hall that there are different “pathways” to a government-run health plan and said there “could” be a role for private health insurance coverage.

Some activists interpreted her remarks as wishy-washy, putting her out of step with the left wing of the party that she was courting.

“The stuff that came out in the spring, we communicated to [Warren’s campaign] staff that we were uncomfortable with the equivocation,” said Stephanie Woolhandler, who has counseled Warren on health policy for several years and is also the co-founder of Physicians for a National Health Program, a single-payer advocacy group. “We advised against equivocating and taking halfway steps.”

The concerns reverberated in Warren’s Boston campaign headquarters, where preparations were underway for the first formal debate of the 2020 campaign cycle set for June in Miami. “The Warren campaign was deeply anxious about Bernie in the weeks before the first Democratic debate,” said someone who talks frequently with Warren’s campaign and was granted anonymity to speak candidly about its thinking at the time.

Among liberals, those fears lifted when, during the debate, Warren’s hand shot into the air in response to a question about who onstage would get rid of the private health insurance industry. “So, yes, I’m with Bernie on Medicare-for-all,” she said.

Rather than settling the matter, new questions emerged.

Warren’s competitors were moving away from the plan. Sen. Kamala D. Harris (D-Calif.), who endured sharp criticism for an earlier answer in which she seemed to support eliminating private insurance, released her own health-care plan in July that allowed a 10-year transition to Medicare-for-all. “I listened to American families who said, “I want an option,’ ” Harris explained days after she made the change.

Buttigieg began rising in the polls. Though he’d tweeted that he was in “favor” of Medicare-for-all in early 2018, during the presidential campaign he repeatedly talked about “Medicare for all who want it” and released a plan in September that would open Medicare to many Americans as a public option but allow private insurance to continue.

By the end of September, Buttigieg was running TV ads in Iowa that contrasted his approach with unnamed rivals who back Medicare-for-all. “Others say, ‘It is Medicare-for-all or nothing,’ ” Buttigieg says in the 30-second spot. “The choice should be yours.”

The industry piled on. The Partnership for America’s Health Care Future, a coalition of hospitals and insurance companies, launched a $1 million TV ad campaign against Medicare-for-all and other changes to health care. Forty percent of it was dumped into Iowa media markets, ground zero for the Democratic campaign, according to data from Advertising Analytics. One spot claimed that “unaffordable proposals” to change health care “could double everyone’s income taxes.” Another claimed that overhaul plans would mean “higher taxes or higher premiums.”

Another group led by Republican strategist Steven Law has spent $5.9 million on TV ads opposing Medicare-for-all, including roughly $650,000 in Iowa, Law said. The ads made a case that wait times for doctor visits would lengthen, a message that caused particular angst for women, Law said.

On the ground in the early states, Warren heard skeptical questions about Medicare-for-all in her public town hall meetings and during private meetings that her staff frequently arranges with key community leaders before she goes onstage. The exchanges were a reminder that many in Warren’s base of largely educated affluent voters might not be ready to give up their private health plans.

“The fact of the matter is, the people who are going to be more likely to show up at her events are going to be people who already have pretty good health insurance,” said Rod Sullivan, a member of the Board of Supervisors in Johnson County, Iowa, who has endorsed Warren. “So when other candidates sow the seeds of doubt with them and say, ‘She’s going to kick you off this. What if it’s worse than what you have?’ Those people are nervous.”

Sullivan recalls standing by Warren in mid-September as she mingled with about 50 people hand selected for a private chat with her ahead of a rally. As these local Democrats came up to talk with her, he said, health care was a constant topic.

“People were saying, ‘Well, I’m concerned about this or that.’ And Warren was reminding people that what you have now is bankrupting you,” he said.

The pressure came to a boiling point when candidates met in Ohio in mid-October for a marathon three-hour debate. It was the first one in which Warren had taken the lead in several surveys — and her rivals came prepared to go after what they saw as a glaring vulnerability. They zeroed in on Warren’s repeated refusal to say whether middle-class taxes would go up.

“Your signature, senator, is to have a plan for everything, except for this,” Buttigieg said.

“At least Bernie’s being honest here and saying how he’s going to pay for this and that taxes are going to go up,” said Sen. Amy Klobuchar of Minnesota, one of several more moderate contenders. “And I’m sorry, Elizabeth, but you have not said that, and I think we owe it to the American people to tell them where we’re going to send the invoice.”

Seven days after the debate, Warren told an audience in Indianola, Iowa, that she would soon release a plan to pay for her Medicare-for-all proposal.

Behind the scenes, Warren’s staff worked frantically to come up with answers, with staffers reaching out repeatedly to academics to test various ideas.

On Nov. 1, Warren released a $20.5 trillion plan that would rely mostly on tax increases on the rich and on companies, her campaign said, adding that it would avoid any tax hikes for the middle class.

Once again, Warren seemed to succeed only in further complicating her political predicament.

While she was trying to reassure the left of her loyalty to the Medicare-for-all cause, she was also promising to carry the fight to the general election by introducing a massive tax on the rich and companies, adding levies that economists argued would be passed on to workers. She was effectively daring Trump, who has expressed eagerness to portray the Democrats as socialists, to paint her as a tax-and-spend liberal who would take away health insurance from millions in her first term.

Centrists pounced.

Former vice president Joe Biden said Warren’s cost estimates were off by trillions. “She’s making it up. There is no way,” Biden said in an interview with “PBS NewsHour.”

House Speaker Nancy Pelosi, who credits a more moderate stance on health care focused on protecting the Affordable Care Act with helping the Democrats take the House in 2018, used a TV interview that day to warn of potential danger ahead for her party — though she did not mention Warren by name.

“I’m not a big fan of Medicare-for-all,” Pelosi told Bloomberg TV, adding: “Hopefully, as we emerge into the election year, the mantra will be, ‘More health care for all Americans.’ Because there is a comfort level that some people have with their current private insurance.”

Two weeks later, on Nov. 15, Warren offered yet another health-care announcement: the “transition plan” that would include an intermediate step letting Americans participate in an optional government-run health plan before an attempt to pass a mandatory program is made.

“By the end of my first 100 days, we will have opened the door for tens of millions of Americans to get high-quality Medicare for All coverage at little or no cost,” Warren wrote in a Medium post. “But I won’t stop there. Throughout my term, I’ll fight for additional health system reforms.”

Warren added, “No later than my third year in office, I will fight to pass legislation that would complete the transition to full Medicare for All.”

It was seen by many on the left as a clear concession.

“You should use the political momentum you have to pass a single plan and use the years in between defending and broadening support for it,” said Mark Dudzic, national coordinator of the Labor Campaign for Single Payer Healthcare, which urges unions to support Medicare-for-all. Dudzic added that he still considers Warren a supporter of Medicare-for-all.

To answer lingering questions about her position, Warren has begun dispatching a policy adviser to Iowa to present the details of her program in small sessions.

The campaign has also worked to line up supporters — which wasn’t always an easy sell.

A key person in validating Warren’s plan has been Rep. Pramila Jayapal (D-Wash.), the House sponsor of the Medicare-for-all legislation, who praised it despite the objections of some members of her staff, according to two people familiar with the discussions.

The congressional staffers have expressed reservations that Warren’s plan would not push for a single-payer system until the third year of her administration, according to these people who spoke on the condition of anonymity to speak frankly of the staffers’ private views about internal talks. Jayapal’s spokesman denied that claim.

Warren’s campaign has tried to describe the three-year delay in pushing for Medicare-for-all as a minor adjustment. At the same time, Warren goes to great lengths to offer reassurance to people that she’s heard their concerns about her earlier position.

At a small town hall in Ankeny, Iowa, on Monday afternoon, Bailey Caskey, a student at the University of Northern Iowa who has committed to caucus for Warren, asked how she could convince her mother on the merits of Medicare-for-all.

For about six minutes, Warren explained — in more detail than usual — how she planned to transition to the system.

“My basic notion has been, we try to get as much help as we can to as many people as we can as fast as we can,” Warren said.

Anu Narayanswamy and Amy B Wang in Ankeny, Iowa, contributed to this report.