With Super Tuesday just days away, a new WBUR poll finds Vermont Sen. Bernie Sanders well ahead of Sen. Elizabeth Warren in her home state of Massachusetts.

The poll shows Sanders is the choice of 25% of likely Democratic primary voters, while Warren is in second place with 17%. The former mayors, Pete Buttigieg and Michael Bloomberg, are in a virtual tie for third at 14% and 13%, respectively. Former Vice President Joe Biden rounds out the top five at 9%.

The new poll is evidence of a big challenge for the Warren campaign, following disappointing results in Iowa, New Hampshire and Nevada. It appears that now the senator faces a tough fight at home.

The WBUR poll of 426 likely voters (topline, crosstabs) was conducted Feb. 23-26, and has a margin of error of 4.9%. (We also polled in the Republican primary.)

According to the poll, Sanders' strength is propelled by younger Democratic voters: almost half of those under the age of 45 say they support the Vermont senator. Warren does well with highly educated voters and women — but overall, she trails Sanders by eight points.

"That's a pretty good size lead," says Steve Koczela, president of the MassINC Polling Group, which conducted the WBUR poll.

Koczela cautions that polls are snapshots of a moment — and not necessarily predictive of what will happen on election day. Lots of people are still making up their minds, and he says this race is still fluid.

"Particularly in primary polling, numbers can change very quickly," he says. "Think back to New Hampshire, where we saw 50% of voters in the Democratic primary who made up their minds just in the last few days."

Warren Ramps Up Operation

The Warren campaign is working hard in Massachusetts, understanding full well that a loss at home would be devastating to a presidential bid trying to regain its footing.

Earlier this week, volunteers launched a canvassing effort in Cambridge, led by Congressman Joe Kennedy III, a Warren backer, who says he is not worried about Warren's fight for Massachusetts.

"I think you've got a long time [to go]," Kennedy says. "March 3rd is an eternity. I believe in her. I think the people here believe in her. I expect she's going to have a great day here, and I think she's going to have a great day across the country."

According to her campaign, Kennedy is one of 147 elected officials from around the state backing Warren, who is also counting on grassroots supporters like Ellen Lawton, of Arlington, who has been canvassing for the senator.

"I think she is the best-equipped to unite all the different members of the Democratic Party, and also to put all the pieces back together again when the [general] election comes," she says.

But Lawton acknowledges that Warren faces a challenge, which she heard about first hand from voters in New Hampshire and Massachusetts.

"Often times I asked them, 'If you had to vote tomorrow, who would you vote for in your heart?' " Lawton says. "And a lot of people say Elizabeth Warren — but they're worried that she's not electable."

In other words, Lawton says they worry that the country is not ready to put a woman in the White House.

"So my message is always, 'We can't elect her if we don't vote for her,' " she adds.

George Snell, from Arlington, agrees — and plans to vote for Warren.

"If she [were] a man she'd probably be so far ahead you couldn't see her," Snell says. "I really like her policies. She's progressive. She's aggressive, and I think she'd make a great president."

Sanders Heads To Boston

The WBUR poll follows a UMass Lowell poll last week that found Sanders with a slight edge over Warren in Massachusetts. Sensing an opportunity for a win on Warren's home field, Sanders plans to campaign in the state ahead of Super Tuesday — with rallies Friday night in Springfield and Saturday in Boston.

Sanders also has the support of a number of elected officials in the state.

"I'm supporting Senator Sanders because of his intentional focus on building a multi-racial, multi-generational, working class movement to defeat Donald Trump," says state Rep. Michael Connolly, of Cambridge, a co-chairman of the Sanders campaign in Massachusetts.

Connolly says his support for Sanders is more about building that movement than voting against Warren — for whom he offers only praise. Sanders is also counting on the support of younger voters like Jonathan Warner, who voted for him earlier this week in Somerville.

"For me the biggest thing was health care," Warner says. "It's ridiculous; there's, what, 30 to 40 million Americans who lack access to health care? So, it seems like we need to overhaul the system."

Warner says he considered voting for Warren, who like Sanders, supports "Medicare for All," which would replace private health insurance with a government-run system.

"I'd be happy with either of them, to be honest," he says. "But I believe that Sanders will do better than her in a general election."

After watching Sanders finish on top in Iowa, New Hampshire and Nevada, Warner says he is now convinced Sanders can win it all in November.

Among the more interesting findings of the WBUR poll relates to the unity — or disunity — of the Democratic Party. It finds that Warren supporters in Massachusetts are the most likely to back another Democrat if their candidate fails to win the nomination. More than 80% of Warren supporters say they'd back any of the other Democratic contenders. By contrast, Sanders' supporters are the least likely to support another candidate. For example, if Pete Buttigieg were to win the nomination, only 44% say they'd vote for him.

"What that means for the party is that if Sanders is not the nominee, the task of bringing Sanders' supporters along to whoever the nominee is will be significant," says pollster Steve Koczela.

That means that if Sanders doesn't win the nomination, many of his supporters might stay home or support a third party. That could hand Trump a big gift in November.