Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) is the candidate with the most momentum as the Democratic presidential field heads into a critical debate on Tuesday.

Warren has surged in front of former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE in recent polls in Iowa and New Hampshire and in some national polls.

She also is seeing some encouraging numbers within the polls.

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Surveys show she has started to appeal to moderate voters and black voters, cultivating a coalition across the party and robbing the Biden campaign of one of its popular talking points.

A Quinnipiac University poll out this week showed that she beat out Biden among Democratic voters and Democratic-leaning independents, 27 percent to 25 percent. She also beat out Biden among somewhat liberal voters, 30 percent to 19 percent.

Among African Americans, Warren has also seen her support rise. A YouGov-Economist survey out this month showed she received 15 percent support from black voters, up from 9 percent in August. And a Monmouth University poll released late last month showed she received 20 percent support from nonwhites, an increase of 6 points from August.

“Warren’s campaign is firing on all cylinders,” said Democratic strategist Jim Manley. “She’s making inroads with voters. and that’s reflected in the recent polls. Not only is she drawing big crowds, but she keeps churning out policy proposals. It’s impressive.”

Warren appears to be on a roll. On Thursday night, she also scored a viral moment during a CNN town hall on LGBTQ rights when she was asked what she would say to a voter who doesn’t support same sex marriage.

“Let’s say you’re on the campaign trail and a supporter approaches you and says ‘Senator, I am old-fashioned and my faith teaches me that marriage is between one man and one woman,’ What is your response?” Morgan Cox, the chairman of the Human Rights Campaign’s board of directors, asked.

"Well, I’m going to assume it’s a guy who said that," Warren said to applause and cheers before adding, "And I’m going to say, 'Then just marry one woman. I’m cool with that — assuming you can find one.'"

In the meantime, Biden has come under fierce attack from Republicans as President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE seeks to fend off an impeachment effort.

Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.), another top-tier candidate, suffered a heart attack and has been off the campaign trail. The health problems have drawn more scrutiny to the 78-year-old senator's age, though Sanders is expected to be at Tuesday's debate.

Democrats — even those who support other candidates — say Warren is exactly where she needs to be at this point in the race, with almost 100 days to the Iowa caucuses.

Over the last six months, she has steadily climbed the polls, slipping by fellow progressive Sanders while drawing arena-sized crowds and creating a fundraising juggernaut strictly from small-dollar donations.

Democrats say Warren is likely drawing support from Sanders but that she may also be winning over more centrist voters.

“While I suspect her momentum is mostly drawing support from people who might otherwise be in the Bernie Sanders camp, I have no doubt that Vice President Biden’s team is tracking her ascendency carefully, as depending on the poll, they are now dueling for front-runner status,” said Democratic strategist Lynda Tran.

Sources close to Biden say they always expected a tight race, but in a possible sign his campaign is worried about the Massachusetts senator, he has started to take some shots at Warren.

“It’s a proven ability to get things done,” Biden said in a speech this week, contrasting his experience with Warren’s. “We’re not electing a planner.”

In the same address in New Hampshire, he also berated Trump for meddling in the Democratic primary by going after him over his son’s business dealings in Ukraine. Biden suggested that Warren’s rise is linked to the attacks Trump and Republicans are making on him, an argument that could help his own cause in the Democratic primary.

“We’re not going to let Donald Trump pick the Democratic nominee for president, period,” Biden said.

Warren allies say they wouldn’t be surprised to see the swipes from Biden continue during the debate on Tuesday. Warren, they say, will be prepared to handle questions about how she plans to pay for "Medicare for All," as Biden wondered during the last debate.

The big challenge for Warren remains convincing enough of the Democratic electorate that she can defeat Trump in the general election.

A Fox News national poll out on Thursday said both Biden and Warren would defeat Trump 50 percent to 40 percent.

But a number of polls earlier in the year showed Biden with a bigger edge over Trump in key swing states. If enough Democratic voters see him as the person with the best chance of defeating Trump, it could carry him to a primary victory.

Manley said Warren still needs to prove herself to voters who may be skeptical of her progressive politics.

“I think she’s still got some work to do to seal the deal with Democratic voters,” Manley said. “Policy positions are nice, but folks are still looking for who can take on this president who has become unhinged.”

“No one has a lock right now on the nomination,” he added.