CONCORD, N.H. — Pete Buttigieg fought back against attacks from three of his rivals while former vice president Joe Biden tried to salvage his campaign with a retooled underdog message Saturday as Democratic presidential contenders careened toward a primary in New Hampshire that could narrow the path forward for several candidates.

Biden, reprising an argument he made in Friday night’s brawling presidential debate, said the former mayor of South Bend, Ind., would put the Democratic Party “at risk” were he to become the nominee.

His campaign put out a new digital ad that derided Buttigieg as a lightweight who dealt with “decorative” issues in contrast to Biden’s role in marshaling landmark Obama administration measures such as the Affordable Care Act and the nearly $1 trillion effort to salvage the economy after the 2008 crash.

“The reports of our death are premature,” Biden shouted into a microphone to a group of campaign volunteers at a campaign headquarters.

Sen. Bernie Sanders (I-Vt.), who effectively tied Buttigieg in Monday’s Iowa caucuses, hit Buttigieg for taking money from wealthy donors.

“If you are serious about political change in America, that change is not going to be coming from somebody who gets a lot of money from the CEOs of the pharmaceutical industry,” Sanders said.

Sen. Amy Klobuchar (Minn.) accused the former mayor of being overly flippant about the seriousness of impeaching President Trump, repeating an attack that she made on the debate stage but also calling out Sanders as a candidate whom Americans are likely to reject.

“When we were asked, ‘Do I think a socialist [shouldn’t] be the one who leads the Democratic ticket,’ I was the [first] one who raised my hand,” Klobuchar said. “People know that I’m straightforward with them and I tell them the truth.”

She, like Biden, was trying to build momentum from Friday’s debate, when she forcefully made her case to be considered by the moderate voters who previously might have been deliberating between Biden and Buttigieg.

Her campaign touted one sign that she had gained some notice: quickly raising $2 million by midday Saturday, according to her campaign.

The increasingly frantic tone of the campaign continued Saturday night at a New Hampshire Democratic Party dinner in Manchester, where, one by one, the candidates made their pitches — as well as the same thinly veiled criticisms they uttered earlier in the day. Supporters on all sides cheered and booed.

The tenor reflected candidates’ frustration that the race has remained stubbornly fluid, with uncertainty more popular than many of the candidates. A new poll showed that roughly half of New Hampshire voters have not definitely made up their minds with just days to go before Tuesday’s primary.

The CNN poll, conducted by the University of New Hampshire Survey Center, showed 28 percent supporting Sanders, 21 percent for Buttigieg and 11 percent for Biden. All other candidates were in single digits, including Sen. Elizabeth Warren (D-Mass.), who was at 9 percent.

The poll findings demonstrated the split among the candidates in the past week. Buttigieg and Sanders were seeking to duplicate in New Hampshire their top-of-the-field showing in the Iowa caucuses. Biden and Warren, who each at one point led in pre-Iowa polling but who trailed the two leaders Monday night, were seeking to avoid a second-straight failure that would call into question their path forward.

No presidential candidate has finished lower than second place in New Hampshire and gone on to become the party’s nominee. For all of the candidates, there was another looming problem: the entrance, as of the March 3 Super Tuesday primaries, of former New York mayor Mike Bloomberg, who has already spent hundreds of millions of dollars in pursuit of the nomination, although he has yet to appear on a ballot or step on a debate stage.

Several of the candidates took on Bloomberg in Friday night’s debate, and Sanders returned to his criticism Saturday.

“We have a former mayor of New York — I won’t mention his name,” he said at an event in Dover, N.H., prompting laughter in the crowd.

Sanders said he has no objection to Bloomberg running for president. “But what in my view he is not entitled to is to buy an election,” Sanders said. “And that is precisely what the corruption of the American political system is about.”

It was Buttigieg’s sudden rise that made him the target of his rivals; he had gained 14 points since Monday in a Boston Globe-WBZ-TV-Suffolk University tracking poll released Friday night, reaching a dead heat with longtime New Hampshire leader Sanders.

Biden’s new ad contrasted his role in the Obama administration with Buttigieg’s former job.

“When President Obama called on him, Joe Biden helped lead the passage of the Affordable Care Act, which gave health care to 20 million people,” says a narrator in the ad. “And when parkgoers called on Pete Buttigieg, he installed decorative lights under bridges, giving citizens of South Bend colorfully illuminated rivers.”

The ad also credited Biden with leading the administration’s successful effort to bail out the auto industry and restore the economy, which it compared to Buttigieg’s action that “revitalized the sidewalks of downtown South Bend by laying out decorative brick.”

As he did in Friday’s debate, Buttigieg pushed back by casting himself as representing both a new generation and a break from the long-standing animosities of Washington.

“I know some folks are out there saying, ‘What business does a mayor of South Bend have running for the president?’ ” Buttigieg said at a stop in Hanover. “ ‘You don’t have an office in Washington, your community is a little out of the way.’ What I’m saying is that’s exactly the point.”

Later in the day, seeming to respond to Biden’s ad, he added: “There are so many communities, rural areas, small towns, industrial cities and pockets of big cities” who feel “left behind by Washington.”

“We’re tired of being reduced to a punchline by Washington politicians,” he said.

Buttigieg had help trying to persuade the undecided voters of New Hampshire. As he emphasized that he was a candidate the country could rally behind, a supportive super PAC, VoteVets, poured roughly $400,000 more into a TV ad campaign running in the state, including spots that feature veterans praising Buttigieg. The group had previously sent $1.3 million to support Buttigieg.

Biden’s refreshed and far more aggressive approach was the result of his departure from the campaign trail for two days, during which he huddled with his advisers at his home in Delaware. He invoked the 1972 car accident in which his first wife and daughter were killed, and the cancer that claimed his oldest son, Beau, in 2015.

“I’ve lost a lot in my lifetime, like many of you have,” Biden said Saturday morning at a Manchester theater crammed with supporters. “But I’ll be damned if I lose my country, too.”

He also spoke with more swagger than he has in recent months, reminding voters of the highlights in his career.

“You guys call these debates? I’ve been in debates. I debated Paul Ryan. I debated that woman from Alaska who said she could see Russia,” he said, referring to his vice presidential debate clashes with former Republican vice presidential nominees Ryan and Sarah Palin, the former Alaska governor.

At another point, he said: “If you notice, I’m still winning nationally. You guys keep forgetting that.”

Biden spared no sympathy for Sanders or Buttigieg.

“Ask yourself, will it be easier or harder to win with a socialist — a democratic socialist, self-stated — at the top of the ticket?” Biden asked, lacing into Sanders.

Buttigieg, he suggested, would also be a gamble.

“I do not believe we’re a party at risk if I’m the nominee,” Biden said during a speech to voters in Manchester. “I do believe we’re at risk if we nominate someone who has never held office bigger than mayor of South Bend, Indiana.”

When it was noted by reporters that Biden’s attacks on Buttigieg echoed the complaint that Hillary Clinton leveled 12 years ago against Barack Obama, Biden interjected.

“Oh, come on, man!” Biden said. “This guy’s not a Barack Obama.”

Asked why he had not addressed Warren, he said: “She hasn’t said anything, if you noticed, in the last month.”

“I respond when people misrepresent my record,” he said. “Elizabeth hasn’t attacked me.”

Sanders, for his part, drew crowds during the day that exceeded 1,000 people. He gleefully told supporters Saturday that “the establishment is beginning to get nervous” about his rise.

“ ‘How do we stop Bernie Sanders and his movement? Oh my god, the people are standing up, fighting for justice, how do we stop?’ ” he said mockingly of his critics.

“Well, they ain’t gonna stop it,” he said, drawing cheers. “We’re on the march.”

Warren, the only top-tier candidate who adopted a strategy of staying clear of the fight, largely maintained that position Saturday, including during Saturday night’s Democratic Party dinner, where she brushed back against the notion that her candidacy was in trouble.

“I’ve been winning unwinnable fights pretty much all my life,” she said.

Warren noted throughout the day that it was the third anniversary of the day she was criticized by Senate Majority Leader Mitch McConnell (R-Ky.) during a lengthy speech she gave on the Senate floor. McConnell’s response — “Nevertheless, she persisted” — became a rallying cry for her supporters.

“Mitch McConnell said those words that a lot of women have put on T-shirts, a lot have embroidered on pillows, a lot have had tattooed on their bodies: Nevertheless, she persisted,” she said at a midday event in Manchester, as the crowd repeated the phrase along with her and applauded.

“The only way we’re gonna make this better is if we use this Democratic primary to build a grass-roots movement,” she said. “Are you ready for some big, structural change?”

She attended a get-out-the-vote event with supporters in Manchester, N.H., and then went door-knocking with her husband, Bruce, and her dog, Bailey.

When asked by reporters about her debate performance, Warren said she wished she had spoken more.

“I thought it went well,” Warren said. “It was a good debate. A lot of back and forth. But I still got to cover issues I care about. Obviously, there’s more I would’ve liked to have talked about. . . . I had my hand up a lot. But you know, I know all candidates want more airtime.”

Michelle Ye Hee Lee, Cleve R. Wootson Jr. and Sean Sullivan contributed to this report.