CHARLESTON, S.C. — The Democratic presidential candidates delivered a barrage of criticism against their party’s emerging front-runner, Senator Bernie Sanders, at a debate on Tuesday night, casting him as a divisive figure with unrealistic ideas, even as they continued to batter Michael R. Bloomberg for his extreme wealth, his record on policing and his alleged behavior toward women.
Mr. Sanders, in his first debate since a smashing victory in the Nevada caucuses last weekend, cut a combative but perhaps not a commanding figure, firmly defending his left-wing agenda on subjects like health care and foreign policy against attacks from all sides. The forum plunged repeatedly into an unsightly spectacle of flailing hands and raised voices, and even outright chaos, with candidates talking over one another and the moderators struggling and failing at times to direct an orderly argument.
But Mr. Sanders said little that seemed intended to ease the concerns of Democrats who do not share his views or who worry that such stances could be politically damaging to the party. And the debate underscored vulnerabilities that are likely to shadow him for as long as the race lasts, and perhaps into a general election against President Trump.
In one striking exchange, Mr. Sanders addressed his record of praising some accomplishments of the Castro government in Cuba by intensifying his denunciations of past American foreign policy, invoking what he called malign intervention in countries like Chile and Iran.
Mr. Sanders also had highly skeptical Democrats sharing the stage with him in Charleston, some of them fighting fiercely for political survival. Former Vice President Joseph R. Biden Jr., who is counting on South Carolina to resuscitate his presidential candidacy, challenged Mr. Sanders on his comments about Cuba and his opposition to certain forms of gun control in an insistent performance that reflected the urgent stakes for his campaign.
Mr. Biden’s determined focus on South Carolina was apparent from the early moments of the debate. He vowed to win the state outright; delivered a lengthy attack on Tom Steyer, a billionaire investor who has spent freely there to woo black voters away from Mr. Biden; and, in the final minutes of the forum, abruptly pledged to appoint a black woman to the Supreme Court.
And when Mr. Sanders invoked former President Barack Obama, arguing that he had gone no further in praising the Cuban system than Mr. Obama did during a visit there, Mr. Biden took issue with that characterization and indicated he had discussed it recently with Mr. Obama himself. Indeed, Mr. Biden and Mr. Obama spoke on Tuesday before the debate, a person briefed on the conversation said.
“I never say anything about my private conversations with him,” Mr. Biden said onstage. “But the fact of the matter is, he, in fact, does not, did not, has never embraced an authoritarian regime and does not now.”
For the first time, Mr. Sanders, a Vermont liberal, also drew pointed criticism from his fellow progressive, Senator Elizabeth Warren of Massachusetts: After spending 14 months as a candidate avoiding direct confrontation with Mr. Sanders, Ms. Warren opened the debate by questioning his record of policy achievements and presenting herself as a candidate who shared his ideas but “would make a better president.”
But it was not clear by the end of the debate that any one opponent stood apart from the pack as the most successful rival to Mr. Sanders, and time is running short for anyone to do so. If Mr. Biden is counting on a surge of support from black voters in South Carolina this weekend to propel him back into contention nationally, the rest of the contenders have even less certain paths forward. They are charting a coast-to-coast scramble for delegates that has left once-surging candidates, like former Mayor Pete Buttigieg of South Bend, Ind., and Senator Amy Klobuchar of Minnesota, falling back on a range of guerrilla tactics to stay competitive.
It was Mr. Sanders, however, who came in for the roughest night. Mr. Buttigieg warned that nominating Mr. Sanders would not only cost Democrats their chance to capture the White House, but also jeopardize their majority in the House and their chance of taking the Senate.
Pointing to the congressional Democrats elected in 2018, Mr. Buttigieg told Mr. Sanders, “They are running away from your platform as fast as they possibly can.”
Mr. Bloomberg, the billionaire former mayor of New York City who is trying to claim the mantle of centrist standard-bearer, joined in, saying of Mr. Sanders: “Can anybody in this room imagine moderate Republicans going over and voting for him?”
As he has done throughout the campaign, Mr. Sanders dismissed the warning about his ability to win over moderates by pivoting to what he views as a strength: his largely untested ambition to drive up voter turnout among constituencies that already lean toward the Democratic Party.
“If you want to beat Trump,” he said, “what you’re going to need is an unprecedented grass-roots movement of black and white and Latino, Native American and Asian, people who are standing up and fighting for justice.”
Mr. Biden, fighting for survival in the state on which he has staked his candidacy, delivered perhaps the most searing critique of Mr. Sanders, invoking the 2015 church massacre here in Charleston to confront Mr. Sanders for his mixed record on guns.
“Nine people shot dead by a white supremacist,” Mr. Biden said, then rebuked Mr. Sanders for his past opposition to waiting periods for gun purchases: “I’m not saying he’s responsible for the nine deaths, but that man would not have been able to get that weapon if the waiting period had been what I suggest.”
The former vice president demonstrated more vigor than at many of the previous debates, when he often seemed somnolent. He sprinkled local references into his comments, sought to interject even when he was not called on and complained when he felt he was not given enough time.
Mr. Sanders and Mr. Bloomberg both answered their critics somewhat sparingly, choosing a handful of attacks to parry without delivering point-by-point rebuttals.
Mr. Sanders acknowledged that he had taken stances on guns in the past that he later came to regret. And he responded forcefully to an attack by Mr. Bloomberg claiming that the Russian government was seeking to buoy Mr. Sanders’s campaign by interfering in the election, citing Mr. Bloomberg’s past laudatory remarks about President Xi Jinping of China.
Addressing the Russian head of government, Mr. Sanders declared, “Hey Mr. Putin, if I’m president of the United States, trust me, you’re not going to interfere.”
Most of all, Mr. Sanders insisted from start to finish that, contrary to the claims of his critics, his ideas were far from “radical,” and pointed abroad for evidence that even his most ambitious proposal — “Medicare for all” — was a mainstream idea in many other countries.
“In one form or another,” Mr. Sanders said of his policies, “they exist in countries all over the world.”
Mr. Sanders was also pressed about his comments on CBS’s “60 Minutes” on Sunday praising the literacy programs enacted by Fidel Castro in Cuba. Plainly irritated, he said he condemned all authoritarian governments but repeatedly returned to a broad denunciation of American aggression in Latin America and the Middle East.
“Occasionally,” Mr. Sanders said at one point, “it might be a good idea to be honest about American foreign policy, and that includes the fact that America has overthrown governments all over the world.”
Mr. Buttigieg used the moment to again raise his claim that Mr. Sanders would be a general election disaster, suggesting that Democrats would be asked why their standard-bearer “is telling people to look at the bright side of the Castro regime.”
On display, too, was Ms. Warren’s dual challenge as she fights for national momentum ahead of next week’s Super Tuesday contests: On the one hand, she is plainly eager to keep up a battle against Mr. Bloomberg that has delighted her supporters and reinvigorated her candidacy. At the same time, she must contend, perhaps more urgently, with the fast and formidable rise on the left of Mr. Sanders — a force she tried to counter by casting herself as a more accomplished progressive.
She pointed to their shared history of battling Wall Street: “In 2008, we both got our chance,” Ms. Warren said, “but I dug in, I fought the big banks, I built the coalitions and I won.”
For the second consecutive debate, Mr. Bloomberg visibly sighed and rolled his eyes as Ms. Warren assailed his variegated political history and demanded fuller disclosure from his company about its treatment of women. Mentioning his history of giving large campaign contributions to Republicans, Ms. Warren said, “The core of the Democratic Party will never trust him.”
Mr. Bloomberg tried to pivot away from Ms. Warren’s criticism to make an argument about his own experience, alluding to his role taking over as mayor of New York after the Sept. 11, 2001, terrorist attacks. “I have the experience, I have the resources and I have the record,” Mr. Bloomberg said, “and all of the sideshows that the senator wants to bring up have nothing to do with that.”
But as in the debate last week, Mr. Bloomberg’s loose phrasing offered Ms. Warren the chance to throw a hard counterpunch: What Mr. Bloomberg called a “sideshow,” she said, involved matters as serious as pregnancy discrimination. She also raised an allegation that he had once pressured an employee to have an abortion, a charge Mr. Bloomberg vehemently denied.
Mr. Bloomberg is not on the ballot in South Carolina on Saturday, but his strength as a candidate in the Super Tuesday primaries next week may depend in large part on whether he can maintain a solid bloc of support among black voters, or whether African-American voters who have drifted away from Mr. Biden over the past month return to his side in the coming days.
Mr. Biden projected confidence when he was asked directly about his support from black voters, the cornerstone of his coalition and a group that will make up over half of the Democratic electorate on Saturday.
“I will win the African-American vote here in South Carolina,” Mr. Biden said, taking care to note he was not taking their support for granted. “I’m here to ask. I’m here to earn it.”
In a sign that Mr. Steyer was making inroads with South Carolina’s black voters, Mr. Biden also took on the billionaire and first-time candidate, noting that Mr. Steyer had invested in private prisons that “hogtied young men.”
Stung by the attack, Mr. Steyer said he had sold his stock in private prisons, then sought to highlight Mr. Biden’s support for the hard-line 1990s crime bill. But Mr. Biden interrupted him and tagged him with a new nickname for changing his mind on private prisons: “Tommy Come Lately.”
Still, Mr. Sanders was clearly the primary target of the night. Ms. Klobuchar also confronted him, boring in on his expansive policy proposals and the risk she said they would pose.
“The math does not add up,” Ms. Klobuchar said, arguing that Mr. Sanders’s agenda amounted to “a bunch of broken promises that sound good on bumper stickers.”
When Mr. Sanders was able to defend himself, he cited studies indicating that “Medicare for all will save money.” But before long he was facing another barb from Mr. Bloomberg, who called the long-term consequences of a Sanders nomination and a Trump re-election a “catastrophe.”
Jonathan Martin reported from Charleston, and Alexander Burns from New York.