MANCHESTER, NEW HAMPSHIRE (NYTIMES) - The two victors in the Iowa caucuses, Senator Bernie Sanders of Vermont and former Mayor Pete Buttigieg of South Bend, Indiana, came under sharp and sustained criticism in a Democratic presidential debate on Friday (Feb 7), as their rivals tried to stop their momentum by assailing Sanders for his left-wing ideas and past opposition to gun control while targeting Buttigieg over his thin résumé and ties to big donors.

In the most contentious debate so far, taking place four days before the New Hampshire primary, the runners up in Iowa charged at Sanders and Buttigieg, who appeared in the best position among the top candidates to win New Hampshire and perhaps take command of the race.

But their opponents, several of whom have significant advantages of their own, showed that they would not give way without a fight: Buttigieg especially came in for bruising treatment, drawing tough challenges from every other candidate onstage, including over his criminal-justice record as mayor and his failure so far to appeal to black and Latino voters.

Former Vice-President Joe Biden, seeking to recover from his limp finish in Iowa, raised the issue of Buttigieg's lack of support among minorities in the opening moments of the debate, saying Buttigieg had not shown he could "get a broad scope of support."

He repeatedly alluded throughout the evening to his own base among African Americans, especially in South Carolina, whose primary is this month and is considered a political firewall if his flagging campaign does not recover before then.

But Buttigieg was not Biden's only target: He also warned that nominating Sanders would taint down-ballot Democratic candidates with the label of socialism, and, in his most blunt attack so far on Sanders, Biden rebuked him for having opposed gun control legislation in the 1990s. Sanders, who has long since disavowed that stance, called it a function of representing "a very, very rural state." The gun issue was a major point of vulnerability for Sanders in his 2016 bid for the Democratic nomination but until now had not been a significant part of the 2020 campaign.

More than a year after the first candidates entered the race, the main divide in the party, whether to enact incremental policy steps or pursue transformational change, was on vivid display throughout the night, and the question of which approach would be more appealing to general election voters was just as divisive.

For Biden, and two other major candidates, Senators Elizabeth Warren of Massachusetts and Amy Klobuchar of Minnesota, the debate was a crucial, and perhaps final, opportunity to reassert themselves in the race and to prevent Buttigieg and Sanders from establishing a tight grip on their respective wings of the party - Sanders on the left, and Buttigieg closer to the political center.

Yet despite the high stakes there were no standout moments of the sort that have transformed past primaries here, and the most aggressive of the seven candidates on the stage, Klobuchar, is polling well behind the New Hampshire front-runners.

Klobuchar, reprising a familiar role as Buttigieg's sternest critic, said he was presenting himself as a "cool newcomer" by dismissing the value of government experience. "It's easy to go after Washington, because that's a popular thing to do," she said. "It is much harder to lead and much harder to take those difficult positions." Klobuchar added: "We got a newcomer in the White House, and look where it got us."

But she was not the only candidate to go after Buttigieg. When the former mayor repeatedly deflected a moderator's question about racial disparities in drug arrests by the South Bend police, Warren said flatly that Buttigieg had not given a substantial answer. "You have to own the facts," she said.

Sanders, too, took on Buttigieg, despite having largely ignored him in previous debates. When Buttigieg attacked his rival's signature health care proposal, known as "Medicare for All," Sanders swiped at Buttigieg's close ties to "big money interests." "Unlike some of the campaigns up here," Sanders said, "I don't have 40 billionaires, Pete, contributing to my campaign."

Even Andrew Yang, the former tech entrepreneur who has rarely used his debate appearances to target his rivals, saw an opportunity to take on Buttigieg. "Pete, fundamentally, you are missing the lesson of Donald Trump's victory," Yang said after Buttigieg denounced the Trump presidency. "Donald Trump is not the cause of all of our problems. And we are making a mistake when we act like he is."

But like Sanders himself, in the moments when he was under attack, Buttigieg gave no ground, arguing determinedly for his own distinctive approach to the 2020 race. He batted away scepticism of his lack of service in the highest levels of government and rejected Sanders' demand for purity in political fundraising. The Trump campaign would be coming at the eventual Democratic nominee with an immense war chest, Buttigieg said, arguing that "we need to go into that fight with everything that we've got."

And in a sign of his confidence in his positioning as a Washington outsider, Buttigieg conceded the point on his lack of traditional qualifications for the presidency, seeming to imply that voters who were looking for a candidate with that profile already had an option in Biden.

"I freely admit that if you're looking for the person with the most years of Washington establishment experience under their belt," Buttigieg said, "then you've got your candidate and of course it's not me."

The debate came at a moment of tumult and anxiety for Democrats, whose leadoff contest in Iowa on Monday turned into a fiasco of technical breakdowns, stalled and fumbled vote-counting and accusations of electoral illegitimacy from multiple presidential campaigns.

On Friday afternoon, Buttigieg and Sanders both claimed victory in Iowa on different grounds, with Sanders brandishing his lead in the popular vote and Buttigieg staking his claim on a hairbreadth lead over Sanders in state delegates, the traditional metric for judging a winner in the caucuses there.

In his first answer of the night, Biden conceded that the political currents were against him in the New Hampshire primary Tuesday and tried to set high expectations for Sanders, who captured the state easily in 2016.

"I took a hit in Iowa and I'll probably take a hit here," Biden said, adding, "Bernie won by 20 points last time."

The discussion of electability was not confined to Sanders and Buttigieg: Warren, hammering at a theme that has come to define her campaign, argued that Democrats could unite their party and win crossover support in the general election by campaigning against corruption. "We can bring in independents and Republicans on that," Warren said. "They hate the corruption as well."

Tom Steyer, the wealthy investor, said the party's nominee had to be able to win support from minority voters, a feat he noted that Buttigieg had not yet managed. By contrast, Steyer added, in an awkwardly clinical turn of phrase, that a recent poll showed that he had "24 per cent of blacks in South Carolina" supporting him.

While the candidates attacked and counterattacked one another with gusto, they saved their most searing critiques for Trump. Biden played to the Democratic-leaning live audience on the campus of St. Anselm College by urging everyone to stand and applaud for Lt. Col. Alexander Vindman, the decorated Iraq War veteran on the National Security Council who testified in the impeachment hearings and was marched out of the White House on Friday. "Stand up and clap for Vindman," Biden said. "That's who we are. We are not who Trump is."

In a series of exchanges on foreign policy, the candidates expressed an overlapping scepticism about the continuing American military involvement in Iraq and Afghanistan. Warren, departing from her usual focus on domestic policy, said she believed it was "time to stop this endless war in Afghanistan," noting without naming names that there were candidates willing to leave troops there for years to come.

"We cannot wait five more years or 10 more years," she said, "or until we turn the corner 10 more times."

Biden, who has faced criticism a number of times, including from Buttigieg on Friday night, for having supported the 2003 invasion of Iraq, said for the first time in a debate that he had disagreed with the Obama administration's approach to Afghanistan.

"I was totally opposed to the whole notion of nation-building in Afghanistan," Biden said, adding that he still believed it was possible to stop "attacks from the region" targeting the United States.

The most sweeping expression of skepticism about military engagement overseas came from Sanders, who stood by his criticism of the US strike that last month killed Qassem Soleimani, the Iranian military commander, which the senator characterised as an assassination.

"You cannot go around saying, 'You're a bad guy, we're going to assassinate you,'" Sanders said, predicting that would lead to "international anarchy." Alexander Burns and Jonathan Martin.