Pete Buttigieg, mayor of South Bend, Indiana, and former Vice President Joe Biden are leading the crowded Democratic presidential primary race in New Hampshire, according to a new WBUR poll. With the first-in-the-nation primary less than nine weeks away, Buttigieg is running slightly ahead of Biden, followed by Vermont Sen. Bernie Sanders and Massachusetts Sen. Elizabeth Warren, who is in fourth place.

It's the latest poll suggesting that Buttigieg has real momentum in Iowa and New Hampshire, home of the first presidential caucuses and primary. According to the WBUR survey (topline results, crosstabs) of 442 likely New Hampshire Democratic primary voters, 18% say Buttigieg is their top choice. The poll was conducted from Dec. 3 to Dec. 8 and has a margin of error of 4.7%. Meanwhile, Biden, after slipping in the polls following some shaky debate performances, is solidly in contention in the Granite State, just one point behind Buttigieg. But the poll suggests the first-in-the-nation primary race continues to be highly unsettled.

"What's remarkable about this is how close it remains," says Steve Koczela, president of The MassINC Polling Group, which conducted the WBUR poll. "We've got three candidates, all within three points of each other — and Elizabeth Warren not that far behind, right there in that top tier. Basically, [this is] a race that could go in any direction."

Moderates Climb

That's especially true in New Hampshire, where voters often deliver last-minute surprises. In fact, when first asked how they would vote, a plurality of likely voters — nearly one in five — say they still have not made up their minds. But Biden and Buttigieg now appear to have an edge in the Granite State, with the former vice president doing particularly well among older voters and voters with a high school education.

Dave Elderkin of Concord, N.H., says he is leaning toward Biden because he believes Biden has the best chance of beating President Trump.

"And the reason for that is we need someone who is in the center," Elderkin said. "I'm a very moderate, pragmatic kind of person, and realize you can't be on either extreme. And he also has the experience."

Democratic presidential candidate and former Vice President Joe Biden reacts while John Kerry, the former secretary of state and 2004 Democratic presidential nominee speaks at a campaign event in Nashua, N.H. on Dec. 8. (Cheryl Senter/AP)

At 77, Biden is 40 years older than Buttigieg. But both are political moderates, who generally promote policies within the current system — a contrast to Sanders and Warren, who are pushing for a "political revolution" or "big structural changes.

Leslie Ring of Bow, N.H., says "she loves" Warren and everything about her — except for one key issue.

"I'm not sure she's electable," she says.

Ring is worried that Warren might be too divisive. So, she's backing Buttigieg.

"I think he brings people together," Ring says. "I think he incorporates religion and policy and intellect. He is hopeful, and he makes you feel hopeful. Especially now, I think that's really important."

Buttigieg casts himself as the candidate best equipped to bring a divided country back together in a post-Trump America. In a recent interview with WBUR, he suggested that Sanders and Warren are too far to the left, particularly on health care. The pair have both proposed a universal, Medicare for All system, and Buttigieg has put forth a more moderate plan that keeps private health care and adds a public option.

"We can do big things," Buttigieg said. "A lot of what I'm proposing would be some of the biggest leaps forward -- for example, on health care -- in a generation, without detonating the kind of divisiveness that we're already seeing happening among a polarized American people."

Warren Slips

Democratic presidential candidate Sen. Elizabeth Warren, D-Mass., holds up 2 fingers as she talks about her two cent tax as she campaigns on Dec. 7 in Rochester, N.H. (Mary Schwalm/AP)

The WBUR polls shows Buttigieg doing well across all age groups in predominantly white New Hampshire, even as he struggles to attract support from black voters in the south. His rise to the top of the field in the Granite State has come as support for Warren appears to have slipped.

Both are competing for highly educated voters, so it's not surprising they are now taking shots at each other. In Peterborough, N.H., Friday, Warren, who has forgone large campaign donations, chided Buttigieg to open up his closed-door fundraisers to public scrutiny.

"He needs to make clear who's raising money for him, who the [campaign donation] bundlers are," Warren said. "And he should open up the doors so that anyone, particularly the press, can come in and hear exactly what's being said to these folks."

Earlier this week, under pressure from Warren, Buttigieg announced that he will open his private fundraisers to the press — while pressuring Warren to release her tax returns from before 2008, when she did private legal work for some big corporations.

According to a number of polls, Warren was leading in New Hampshire earlier this fall. But she faced pressure from Buttigieg, among others, to explain how she planned to finance her Medicare for All proposal. She did, unveiling a massive $20.5 trillion plan, that would raise taxes on corporations and the wealthy.

"It was about the time that she rolled out the Medicare for All plan in some detail that her momentum seemed to fade a little bit," says Koczela.

But correlation is not causation. Koczela says a number of factors could explain Warren's slump in the polls, including the fact that as a front-runner she drew fire from her competitors and more scrutiny from voters.

As Warren's campaign seems to have hit some turbulence, her fellow progressive, Sanders, has rebounded, and holds a loyal base.

"He speaks to the people," says Rebecca Shersnow of Phillipston, Mass., who attended a Sanders rally in Keene, N.H. "He's great because if you look at what he was saying in the '80s and '90s — that hasn't changed. He's a real person, and I can believe in him. And you can't say that about a lot of politicians."

Democratic presidential candidate Sen. Bernie Sanders, I-Vt., high-fives supporters as he arrives at a campaign stop on Nov. 24 in Hillsboro, N.H. (Mary Schwalm/AP)

The WBUR poll finds a dramatic age gap between Sanders' supporters and those of Biden. Close to a third of voters 18 to 29 prefer the Vermont senator, but he is the choice of only 6% of voters over 60. The age preferences flip with Biden: he has the support of nearly a third of voters over 60 but only 3% of younger voters. So it seems that younger voters are more open to a "political revolution," while older ones want a return to the normalcy that Biden promises.

Republican Challengers Struggle

The new WBUR poll (topline results, crosstabs) also finds President Trump is still immensely popular among New Hampshire Republicans, and he maintains a yawning 60-plus-point lead on both his primary challengers.

The survey, of 365 likely Republican primary voters, found 74% say they’re leaning toward casting their ballot for Trump in the N.H. primary, amid the impeachment proceedings on Capitol Hill.

Just 9% of likely Republican primary voters support Bill Weld, the former governor of Massachusetts.

“That’d be a really good number, if he were in the Democratic primary,” says Koczela. “He’s not really giving Donald Trump any sort of scare at the moment, but he is actually polling numbers that could mean that he ends up getting a decent number of votes."

At the same time, Trump’s favorability rating appears to have taken a hit in the state: WBUR’s poll finds 71% of likely Republican primary voters view the president favorably, down from 85% in an October poll from CNN and the University of New Hampshire.

Weld, who ran for vice president on an unsuccessful libertarian ticket in 2016, is campaigning on a platform of fiscal responsibility and “a government that stays out of your wallet and out of your bedroom.”

President Trump’s other challenger, Joe Walsh, is polling at just 4%. A conservative talk radio host and former “Tea Party” congressman from Illinois, Walsh supported the president in 2016, but now says Trump “deserves to be impeached.”

WBUR's Wilder Fleming contributed to this report.