WASHINGTON — Joseph R. Biden Jr. on Tuesday pressed his case that he is the “most electable” Democratic presidential nominee, saying that while his primary rivals may draw large crowds in urban centers or excite young progressives, he retains the most racially diverse coalition of supporters.
The argument, bolstered by Mr. Biden’s strong poll numbers among black voters, accentuates the central thesis of his candidacy: that he is the Democrat most capable of beating President Trump.
It also comes as the Democratic field has winnowed in recent weeks, with some polls showing the race as increasingly a battle of three candidates — the more moderate Mr. Biden and the race’s two progressive New England senators, Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts.
With that new landscape coming into focus, and with Mr. Biden facing scrutiny for a series of verbal slip-ups on the campaign trail, he and his team have leaned more into his support from black voters than ever. They have sought to cast their progressive rivals as representative of an elite class of Democrats that skews whiter, more educated and younger. They have also sought to counter critics who have tried to paint Mr. Biden’s candidacy as one-dimensionally focused on the white working class.
“The bad news is that I have a long record, but the good news is that I have a long record,” Mr. Biden said in an interview with a group of black journalists. “People know me, or at least they think they know me, after all this time. They have a sense of who my character is and who I am — warts and all.”
Black voters are more moderate, Mr. Biden argued, and particularly the older ones who make up a large portion of the Democratic electorate in Southern states. This serves him well, he said, because “that’s kind of where I come from.”
Mr. Biden’s communications director, Kate Bedingfield, made a similar argument in a television interview Tuesday. “No Democrat is going to win the nomination for president of the United States without African-American support,” she said. “And nor should they.”
“I have never, ever, ever, in my entire life, had a circumstance where I have felt uncomfortable in the black community,” Mr. Biden said in the group interview. He said the same was not true of some liberals.
“There are assumptions made about the black community that I don’t think are accurate,” he said, and “that’s partly because they haven’t spent much time in the black community.”
The interview with Mr. Biden, which was conducted in Washington and lasted more than 90 minutes, covered a wide range of topics. At one point, he criticized another Democratic candidate, Senator Kamala Harris of California, for what he thought was an unfair attack on his record on race during the Democratic debate. He also criticized her campaign’s policy proposals for relying heavily on executive orders instead of legislation.
He also used the forum to harshly criticize Mr. Trump, asking the group to imagine if a school principal used some of Mr. Trump’s words.
“The first thing you’d do is to go in there and make sure that son of a bi — that person — was fired,” Mr. Biden said, quickly correcting himself.
Mr. Biden repeatedly argued that Mr. Trump had inspired racism in America through bigoted speech and nativist policies, but he did not answer a question from The New York Times about whether Mr. Trump was himself a white nationalist. Aides later pointed to a speech he gave earlier this year, when he said Mr. Trump “fanned the flames of white supremacy,” but avoided using such a label to describe the president himself.
In another part of the interview, Mr. Biden said there were “three categories” of white people when it comes to race issues in America.
“There are those who are flat-out just prejudiced, who are supremacists of some degree. There are some who are agnostic and don’t give a damn about it and just go, and there’s folks who want us to do something about it,” Mr. Biden said.
Asked why Republicans would work with him as president, when they repeatedly blocked President Barack Obama’s policy proposals, Mr. Biden said he would be able to apply unique political pressure on Republicans because he could appeal directly to their voters.
“Part of the role of a president is to persuade,” he said. If Mitch McConnell, the Senate majority leader, were to block him, he said, “Guess what? I’m going to go to Kentucky, and I’m going to campaign.”
Polling in recent days has given hope to both Mr. Biden’s camp and the Sanders-Warren wing of the party. A much-talked-about poll published Monday showed the race as a virtual three-way tie. But Mr. Biden’s pollster, John Anzalone, quickly called the poll an outlier.
Other polling has shown Mr. Biden comfortably ahead, including among black voters. But in early-voting primary states, and particularly in Iowa, the race has often appeared fluid, with months to go before the first votes are cast.
In his comments, Mr. Biden acknowledged the unpredictability of the nomination contest, drawing a comparison to Mr. Obama’s victory in Iowa in 2008.
“I got blown out in Iowa, and all of a sudden, everything changed,” Mr. Biden said. “Barack clobbered me.”