MANCHESTER, N.H. — Elizabeth Warren came here in force.

Democrats at Southern New Hampshire University Arena erupted as she took the stage, supporters slamming thunder-sticks that read “Win with Warren” and delaying her speech with two minutes of cheering. They chanted “two cents” as the Massachusetts senator detailed her 2% “wealth tax” on fortunes larger than $50 million, and a battalion of backers roamed the concourses in mint green Warren T-shirts, easily outnumbering any rivals.

As 19 Democratic presidential candidates pitched themselves to thousands of activists, the scene Saturday illustrated why many in the party believe Warren has built more new energy than anyone else, vaulting her into the top tier with former Vice President Joe Biden and Vermont Sen. Bernie Sanders.

With another presidential debate looming Thursday on ABC, polling and interviews show that Warren has emerged not only as a liberal alternative to Sanders, but increasingly as a potential threat to the front-runner, Biden — especially for Democrats looking for a more dynamic and fresher leader.

“She’s one of the few candidates in a long time that I feel I can trust,” said Megan Peterson, a Walpole, Mass., resident who made the trip to Manchester to support Warren.

“She has really kicked ass and run an outstanding campaign,” said Mike Lux, a Democratic strategist who worked for Biden’s 1988 campaign. “There’s plenty of impressive candidates who’ve done some interesting things, but the one who seems to have staying power in terms of the challenges to Biden, it seems like its been Elizabeth.”

If Biden represents the party’s pragmatic side and Sanders its liberal restiveness, Warren’s supporters in New Hampshire argued she combines both.

“She may be progressive, but she’s got a plan, and I like that’s she’s got a plan and she can tell you how you’re going to get there,” Marcia Hayward, 69, said after attending a Biden event in Laconia, N.H. She was “torn” between Warren and the former vice president.

The two will appear on stage together for the first time during Thursday’s debate, setting up one of the most anticipated contrasts of the early campaign.

While Biden and Sanders began the race with name recognition and national followings, and remain at or near the top of the polls, each have dipped from earlier highs. Warren, meanwhile, started with a stumble over her claims of Native American heritage but has been the only candidate to steadily rise, moving into a tight race with Sanders for second place and drawing growing crowds.

She may also be surging in New Hampshire: an Emerson College poll released Tuesday showed her rocketing into second place there, with 21% support, more than doubling her total from February, while Sanders tumbled to third in the survey.

In interviews with 44 New Hampshire Democrats last weekend, those behind Biden frequently turned to sober words like trust and experience, and calculated that he is best positioned to win swing voters. Much of his visible support at the Manchester convention came from a bloc of union firefighters. Sanders loyalists praised his unstinting message and leadership in moving the party leftward.

Warren supporters said they could relate to her backstory, growing up poor in Oklahoma, being a single mother and going on to teach at elite law schools after attending Rutgers Law. They described her as detailed and progressive but with a more upbeat and practical style than Sanders.

“We need energy, and she gave it to me,” Diane Foley, 70, said in Portsmouth as she recounted seeing Warren earlier in the campaign.

In an online poll of Democrats in 18 early voting states, 46% would be excited by a Warren nomination, against 38% for Sanders and 29% for Biden, CBS/YouGov found. More Democrats named her as their first choice than anyone else (though she was only 1% stronger than Biden), according to the survey, completed last week.

However, she trailed Biden and Sanders in three of the first four primary and caucus states, and polling by Morning Consult shows that Biden supporters are slightly more likely to pick Sanders as their second choice than Warren.

The liberal senator has built her campaign around a relentless public schedule (129 town halls, she said) and a stream of detailed policy ideas, explained in human and digestible terms by a former law professor. In her speech Saturday, Warren said the first $50 million of anyone’s assets would be free from her tax plan — and wiped her brow for comic effect.

“There’s a joyfulness that comes with Warren as opposed to the straight doom and gloom with Sanders,” said John Lapp, a Democratic consultant based in Washington, D.C.

Sanders and Warren appear on a collision course as they compete to represent the party’s liberal wing and to win New Hampshire, the second state in the nominating contest and one they both claim as a neighbor.

Still, the two have avoided conflict with each other, endorsed many of the same policies, and many of their supporters in New Hampshire expressed admiration for both.

Perhaps more surprising, Warren has also made inroads with more centrist Democrats, including some in the donor class who view her as more electable and less hostile than Sanders.

» READ MORE: Elizabeth Warren ripped Joe Biden’s big Philly fund-raiser. Last year, she did an event with some of the same rich donors.

Yet, even some who like Warren worried she may be too liberal for the swing states that could decide the race.

“I agree with so many of her policies,” said Hilda Slivka, 65, who attended the Biden event in Laconia. “I just think he [Biden] can garner more votes than she can. We’ve gotta win.” She hoped for a Biden-Warren ticket.

Sanders supporters point to his dominance in small donations and leadership on Democrats’ top policy issue, health care, as evidence of his strength, along with his own raucous reception in Manchester. Biden’s campaign has touted the breadth of his coalition, emphasizing his support from the white working class, black voters, and Hispanics. Warren’s backing skews whiter, wealthier, and more college-educated.

» READ MORE: Bernie Sanders got more small donations in Pa., N.J. than Elizabeth Warren and Joe Biden combined

Some Democrats also argue that ideas alone won’t win, suggesting that Warren may face new criticism as she climbs.

“We need candidates … that are going to speak to the guts and the heart and the soul of people,” New Jersey Sen. Cory Booker told Democrats at a Nashua, N.H., coffee shop. “Because the person with the best 15-point policy plan is not the person that wins. If it was, we would have won the last presidential election.”

Warren, in her speech, acknowledged the concern gripping Democrats who may be afraid of pushing too far left.

“I get it, there is a lot at stake. And people are scared," she told the crowd. "But we can’t choose a candidate we don’t believe in because we’re scared, and we can’t ask other people to vote for someone we don’t believe in.”