MANCHESTER, N.H. — Joseph R. Biden Jr. and Senator Elizabeth Warren each suffered a damaging setback in Iowa that could make it harder for them to recover next week in New Hampshire — and not just because they were running well behind the leading candidates as Democrats awaited a final count.
In a primary sharply divided between progressive and more moderate candidates, Mr. Biden and Ms. Warren both trailed opponents with whom they are competing for many of the same voters.
The former vice president was badly beaten in the fight for center-left Democrats by Pete Buttigieg, according to the still-incomplete Iowa caucus returns, while Ms. Warren was significantly outpaced among left-wing voters by Senator Bernie Sanders.
“Each underperformed expectations in Iowa, and a second week of disappointing results could have a dire impact on money moving forward,” said David Axelrod, the Democratic strategist.
Yet as Mr. Biden and Ms. Warren look to revive their campaigns in New Hampshire and stop their ideological rivals from gaining momentum, they are adopting strikingly different approaches that could both prove perilous.
Badly outspent on the airwaves here, Mr. Biden has started taking direct aim at both Mr. Buttigieg and Mr. Sanders in a revamped stump speech, a first for a candidate who has led the field in most national polls and largely focused his fire on President Trump. Ms. Warren, however, is amplifying her message about being the Democrat who can unify a badly fractured party but is so far avoiding direct criticism of her rivals.
Mr. Biden risks coming off as overly negative, always a gamble in a multicandidate race where third parties can benefit from such attacks. But there are dangers for Ms. Warren as well, if she appears to be acting without enough urgency, given Mr. Sanders’s lead in New Hampshire polls and the expectations she faces coming from next-door Massachusetts
What the two candidates are united by, however, is a shared hope that New Hampshire will not spell their demise: Both Mr. Biden and Ms. Warren are working strenuously to shore up their standing in Nevada, which votes on Feb. 22, and the similarly diverse states in the weeks that follow.
Mr. Biden and his top advisers made no effort to hide their disappointment about Iowa on Wednesday — and they plainly recognize that he must finish closer to the top in New Hampshire if he is to remain in contention by the time Super Tuesday rolls around early next month.
Speaking in Somersworth, N.H., on Wednesday morning, the former vice president demonstrated that he recognized his position is perilous.
“I am not going to sugarcoat it, we took a gut punch in Iowa,” Mr. Biden said. But then he offered a more confident message to those he said were already moving to “write off” his candidacy.
“I’m not going anywhere,” he said, adding: “I’m counting on New Hampshire. We’re going to come back.”
And he signaled that to do so, he is going to directly confront two of his rivals.
“Donald Trump is desperate to pin the socialist label of socialist, socialist, socialist on our party,” Mr. Biden said, alluding to Mr. Sanders, a self-avowed democratic socialist. He argued that every Democrat on the ballot “will have to carry the label” in November.
Similarly, Mr. Biden warned that elevating Mr. Buttigieg could hand Mr. Trump four more years.
“I have great respect for Mayor Pete and his service to this nation,” Mr. Biden said. “But I do believe it’s a risk, to be just straight up with you, for this party to nominate someone who’s never held an office higher than mayor of a town of 100,000 people in Indiana.”
William Shaheen, a longtime Democratic activist in New Hampshire who spent time with Mr. Biden Wednesday, said he was happy that “Joe has got his Irish up,” as he put it.
“We talked about fire in the belly,” Mr. Shaheen said. “He says, ‘I got it, don’t worry.’”
Privately, Mr. Biden’s advisers are targeting Mr. Buttigieg even more aggressively. In talking points sent Tuesday night to some of their leading supporters, and shared with The New York Times, the campaign highlighted what they hope will be their political salvation.
“After a year of running for president, he hasn’t been able to get ANY support from African-American voters,” the document said of Mr. Buttigieg, noting that he had garnered zero percent among blacks in a recent national poll. “How do you win the Democratic nomination if you can’t get any diverse support?”
At Mr. Biden’s Philadelphia headquarters, his aides braced Wednesday for staff changes, and grumbling intensified about the generational gap between some of the candidate’s younger aides and its older fixtures, according to Democrats familiar with the tension. There are concerns about the differences between the campaign manager, Greg Schultz, and the longtime Biden adviser Steve Ricchetti, in particular, these people said, and some aides believe that Mr. Ricchetti unrealistically raised expectations internally about what was possible in Iowa.
Outside the inner circle, Biden supporters said the confusion over the reporting of Iowa results helped mitigate his dismal finish but also signaled a recognition that Mr. Biden has to improve his standing in New Hampshire on Tuesday.
“If he doesn’t do well in New Hampshire, the media will think that’s the end, because it’s always been the end,” said Ed Rendell, the former Pennsylvania governor, though he said he did not believe that would hold true this year.
More crucial for Mr. Biden and Ms. Warren, however, may be Nevada, the first contest with a large share of minority voters. Mr. Biden this week cut his advertising spending in South Carolina and redirected more money to the airwaves in Nevada.
Yet it is possible that two of the most influential forces in the state’s politics may remain on the sidelines before their caucuses. Former Senator Harry Reid, long the de facto leader of the Nevada Democratic Party, said that despite “encouragement from a number of my friends,” he still planned to stay out of the race.
Just as important, the politically muscular culinary union in Las Vegas also may not endorse before the caucuses, Mr. Reid said.
“They’re keeping their powder dry,” he said. “They may wait until after the caucuses.”
Both Mr. Biden and Ms. Warren have aggressively courted Mr. Reid and the union, which represents many of Las Vegas’s casino workers, and Ms. Warren is planning to dispatch one of her top labor allies from Massachusetts to help her in Nevada.
Yet she and her top aides do not think they are in as precarious a position as Mr. Biden because Iowa’s delay in reporting results denied Mr. Buttigieg and Mr. Sanders the momentum that usually accompanies a top finish there.
But after her campaign claimed Monday night that Iowa had produced a close race among the top three contenders with Mr. Biden trailing well behind, it became clear by Wednesday that Ms. Warren was running significantly closer to Mr. Biden than she did the top two vote-getters.
With Ms. Warren having built a vaunted statewide organization and enjoying an electoral base heavy on the white liberals that dominate Iowa’s caucus electorate, her performance illustrates the ideological squeeze she finds herself in. Mr. Sanders has coalesced support among many progressives and young voters, while Mr. Buttigieg has established himself as the foremost alternative to Mr. Biden among moderates in the early states.
Addressing reporters in Nashua, N.H., on Wednesday, she sought to put the best face on Iowa while suggesting she would stay in the race no matter what happens here next week.
“We’re in the top three in Iowa and now we’ve landed in New Hampshire and now we’re out there fighting for everyone in New Hampshire and then after that we have 55 more states and territories,” Ms. Warren said.
In her remarks to supporters in Nashua, she made no direct mention of her rivals, only nodding implicitly at the risk of nominating Mr. Sanders with a line that she began reciting in Iowa. “We’ve got to pull our party together,” Ms. Warren said. “We cannot repeat 2016.”
Ms. Warren’s advisers, some of whom concede privately that she was disappointed with Iowa, dismiss the possibility that she would make any organizational changes. She plans to keep emphasizing how she can bring together both flanks of the party while highlighting her history-making potential to be the first female president.
But with Senator Amy Klobuchar of Minnesota remaining in the race and winning a place on the New Hampshire debate stage Friday, Ms. Warren’s gender appeals may be diluted.
“I do know a lot of women who are saying they want a women nominee and they’re deciding between Amy and Elizabeth,” said Kathy Sullivan, a former New Hampshire Democratic chair.
Thomas Kaplan contributed reporting from Somersworth, N.H.