Sen. Elizabeth Warren (D-Mass.) has been mostly sure-footed in her campaign for the Democratic presidential nomination. One exception is health care. On Friday, she issued another proposal to go along with her support for Medicare-for-all, a step that appeared designed to put her into a safer place politically.

Warren’s progression on health care through the course of the campaign has taken her from a position of flexibility to one of seeming inflexibility — at least until Friday. Over a period of months, she walked herself into a place that many Democrats feared could make her chances of winning a general election more, not less, difficult. Whether Friday’s turn alleviates those worries remains to be seen.

From the start, Warren’s mantra as a candidate has been her advocacy of “big structural change” to rebalance a system she says is tilted to the biggest corporations and to the wealthy and the well-connected rather than the rest of society.

She issued a series of plans covering things such as child care and college costs and housing, ambitious and costly initiatives that she said would pay for with a new wealth tax on people with fortunes of $50 million or more. She promises to take on the big banks and drug companies and the tech giants. She supports political reforms that would diminish the power of special interests and big money in politics.

One piece was always missing in those early days. That was a health-care plan. Warren has sought to bring rigor to her policy proposals, and as every candidate and president has learned, health care is the knottiest, most complex and seemingly insoluble of the big issues. She seemed in no rush to put her own stamp on a plan until she was ready.

Like all the candidates for the Democratic presidential nomination, she shared the goal of assuring universal and affordable health-care coverage to all Americans. She was for Medicare-for-all rhetorically but hesitated to offer her own distinctive plan, perhaps knowing that this could be a 10-year project and one that might be done in small steps or in a big bang.

During a CNN town hall meeting in March, she said, “When we talk about Medicare-for-all, there are a lot of different pathways. What we’re all looking for is the lowest-cost way to make sure that everybody gets covered.”

She took a fateful step away from that position during the first Democratic debate in June in Miami. Asked by NBC News’s Lester Holt who would support eliminating private insurance, she raised her hand. Moments later, she cast her lot with Sen. Bernie Sanders (I-Vt.), who has long been the most vocal advocate of replacing the current employer-based insurance system with a single-payer government-managed system. “I’m with Bernie on Medicare-for-all,” she said that night.

That helped to widen a fault line in the Democratic field between those like Warren and Sanders, who were calling for the elimination of private insurance, and those like former vice president Joe Biden and others, who proposed building on the Affordable Care Act by adding a public option but not jettisoning the current structure.

Warren further isolated herself by declining to explain how she would pay for Medicare-for-all — in contrast with Sanders. The senator readily acknowledged that, under his proposal, middle-class families would pay higher taxes. But he argued that the shift to a single-payer system would result in lower overall costs to those families for their health-care coverage and therefore was well worth it.

Warren, under repeated questioning and criticism from her rivals, would not answer directly. She tried to deflect by saying that she would not sign a plan that would mean higher health-care costs for middle-class Americans. To her critics and even some of her supporters, it was an evasive and unsatisfying answer, particularly coming from someone who had detailed answers to questions about her other proposals.

Then a few weeks ago, just before a big Iowa Democratic Party fundraising dinner that drew all the candidates, Warren answered her critics by issuing a financing plan for Medicare-for-all. She had experts who vouched for the soundness of the financing plan, but other experts picked it apart as unrealistic, based on some overly rosy assumptions. To the broader audience of Democrats, it didn’t pass muster.

For those with doubts about her viability as a general election candidate, the proposal only added to their worries. Politically it fell far short of what she might have hoped. It opened her up to fresh charges that she was advocating a health-care plan that lacks majority support in the country and didn’t have a sound plan to pay for it.

Many in her party worried that if she became the nominee, she would be handing President Trump’s reelection campaign ammunition on an issue — health care — that long has been more favorable to Democrats

Conversations with Democrats over the past two weeks have underscored the degree to which the whole issue was becoming a potential obstacle to a campaign that otherwise has been doing many things right. “It froze a lot of people,” a still-uncommitted New Hampshire Democrat said last weekend.

Warren has prided herself on being a fighter for the causes she believes in, and she and her campaign team have aggressively pushed her health-care plan, even at the doorstep with voters. One Democrat said that a Warren field organizer knocked on his door recently and during the conversation initiated a defense of her plan and explained why she could win a general election with that position.

All of which makes what Warren did on Friday potentially significant. In short, she said that in her first 100 days she would try to enact legislation that would allow, but not require, Americans to purchase a government health-care plan — in other words, a public option akin but not identical to those proposed by Biden; South Bend, Ind., Mayor Pete Buttigieg; Sen. Amy Klobuchar (D-Minn.); and others.

Warren also said that she would wait until the third year of her presidency to begin to enact a Medicare-for-all plan, a more gradual approach than she had seemingly described in the past and one would allow her to try to build public support before plunging into something as daunting as this would be.

Warren will try to argue that the changes she proposes during the transition period are more ambitious than those of her rivals, in keeping with her pledge to be the candidate of big structural change. But she already has come under criticism for a change in positions and will face many more in the weeks ahead as she tries to explain the evolution of her thinking.

What Warren did on Friday could help to ease the fears of Democrats that she would be a vulnerable general-election candidate advocating positions that are politically unpalatable. But she is a long way from becoming the nominee. Medicare-for-all proved to be a problem for her and, while she may be on slightly safer ground today than a week ago, she hasn’t fully solved the problem.