LAS VEGAS — Elizabeth Warren's longstanding truce with Bernie Sanders came apart in the days before the Nevada caucuses. But the push came too late, with her campaign now on life-support after disappointing finishes in the first three states to vote.

Sanders, the independent senator from Vermont, won a dominant victory in Nevada on Saturday, with Warren coming in fourth after she spent the preceding week throwing caution to the wind, for the first time making an explicit case for why Sanders should not be the Democratic presidential nominee.

She took him to task for a lack of transparency on his health records, for the ugly behavior of some of his supporters, for refusing to call for abolishing the Senate filibuster, and for his campaign's negativity toward others on "Medicare for All." She even criticized him by name after months of contrasts that were too subtle to make an impression on many voters.

Some Democrats wonder why she waited so long.

"Her strategy failed her. Her strategy failed her, and she clearly changed her strategy this week," said Mary Anne Marsh, a Democratic consultant in Boston, in Warren's home state, Massachusetts. "She didn't do the contrast strongly enough until the last week or so. ... The debates in Iowa and New Hampshire — they certainly seem like missed opportunities given what she was able to do in the debate last week."

"She needs to say: If you really want progressive things to happen in this country and you want to get them done, I'm the progressive who can get them done. And draw that contrast with Sanders," Marsh said. "Her campaign was built on adversity and she's done it before," she said. "You can't count her out to do it one more time. But she's got eight days to do it."

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After launching her campaign last year, Warren cultivated a core base of educated Democrats and people who want a woman elected president. She avoided criticism of rivals and ran a policy-focused campaign that conveyed her vision for rooting out corruption and bridging income inequality. The strategy was paying dividends, and by early October she had surged to front-runner status in some surveys.

Then Sanders began a comeback after his heart attack in October, fueled by a consequential endorsement from progressive icon Rep. Alexandria Ocasio-Cortez, D-N.Y. As he consolidated liberal voters in the weeks before the Iowa caucuses, Warren softened her message to emphasize party unity, which seemed to undercut the image of a progressive "fighter" that had fueled her rise in the first place.

Last week, Warren finally dispensed with her genteel "unity" message and delivered a tour de force debate performance Wednesday that spared none of her four main rivals. She criticized Sanders for running a campaign that "relentlessly attacks everyone who asks a question or tries to fill in details about how to actually make" his Medicare for All plan work.

At an event in Las Vegas on the eve of the caucuses, she questioned Sanders' commitment to progressive change by criticizing his resistance to ending the 60-vote rule to pass Senate bills.

"When other people who are running for president — and I say this just as a factual statement — like Bernie, who say they want to make real change but they will not rollback the filibuster. Keep in mind what that means, they have given a veto to the gun industry to prevent real change and gun reform. A veto to the pharmaceutical industry, a veto to the insurance industry," Warren said. "We cannot, cannot, cannot give a veto to those who want to block real change in this country."

Warren was finally giving progressive voters a reason to support her over Sanders. Politically, her campaign attracts more mainstream Democrats who don't want a democratic-socialist nominee. And she sweats the details of policy and thinks about how to get from point A to B. And she called on Sanders, who is 78, to release more medical records after his heart attack.

"Any candidate who wants to win this primary, Warren included, should see the writing on the wall: Bernie is going to run away with this thing unless they go directly after him," said Ian Sams, who faced Sanders twice as a former aide in Hillary Clinton's 2016 campaign and Kamala Harris's 2020 bid.

"Even then, it’s an open question whether it will work at this point. He has been able to not only consolidate a base but expand his appeal to new demographics over the past few months, largely unchallenged by his competitors. Looking back, candidates should have gone after him starting in the fall, recognizing he had a strong structural position as the front-runner."

In a country that has never elected a woman president, Warren's advisers have long recognized that she faced a unique challenge when it comes to being combative. In an interview on Monday, she suggested there was a double standard for women who are quick to be seen as too aggressive.

"This is what women face all the time. It's always too much of this, too much of that," Warren told NBC News. "But you put your head down, you do your job, and you keep on going or you might say, we persist."

Brian Fallon, a Democratic strategist who worked on Clinton's 2016 campaign, said "never Bernie" Democrats "are panicking right now" and may have erred by circling "the wagons against Warren in October" when they had a chance to stop him.

"They may end up having buyer's remorse because Warren may have been a more viable non-Bernie candidate than Pete (Buttigieg) or (Joe) Biden," he said.

Conceding the Nevada caucuses on Saturday night, Warren again went after Sanders, saying there's "no magic wand" to getting big things done and suggesting she has a more viable strategy.

"People ask me about differences between Bernie and me. I want to point out a big one," she said. "You want to get something done? Bernie says we're going to keep the filibuster. I say Mitch McConnell is not going to get a veto over what we want to do."