WASHINGTON — Joseph R. Biden Jr.’s presidential campaign was under attack, and he and his advisers were torn over what to do.
For more than a week, President Trump had been hurling unfounded accusations about Mr. Biden, his son Hunter and their dealings in Ukraine. Mr. Biden and his advisers debated whether to mount a fierce counterattack or to stick to a set of policy arguments he had been planning to roll out. Bad news loomed in the background: Mr. Biden’s poll numbers had already grown wobbly, his fund-raising was uneven, and cable news was flashing chyrons by the hour showing Mr. Trump’s wild claims.
Mr. Biden himself was equivocating: He wanted to defend and protect his son, but he also believed the president was baiting him into a dirty fight. And as a lifelong adherent to congressional tradition, Mr. Biden was wary of acting hastily as an impeachment inquiry was getting underway.
The strain grew so acute that some of Mr. Biden’s advisers lashed out at their own party, taking the unusual step of urging campaign surrogates to criticize the Democratic National Committee — a neutral body in the primary — for not doing more to defend Mr. Biden, while the Republican National Committee was running TV ads attacking him. Frustrated, D.N.C. officials informed the Biden camp that it would continue denouncing Mr. Trump but would not run ads for Mr. Biden or any other candidate.
The Biden campaign’s tense deliberations reached a climax last weekend when Mr. Biden agreed to give a scorching rebuttal to Mr. Trump in a speech on Wednesday in Reno, Nev. But he delivered it well into the evening on the East Coast, and it was mostly lost amid another long day of Trumpian eruptions.
To some Biden allies, it seemed too little too late: a case study in political indecision. Now Mr. Biden looks more vulnerable than at any point since he entered the campaign. Facing one of the greatest challenges of his candidacy, Mr. Biden has plainly struggled to meet the moment, or fully reconcile his own cautious instincts with his protectiveness of his family’s privacy and his preference for taking the moral high road against Mr. Trump.
Interviews with more than 50 Democratic strategists, lawmakers and lobbyists provide a portrait of a candidacy facing challenges on all sides, and one at risk of losing its core argument that Mr. Biden is the Democrat best able to defeat Mr. Trump in a general election.
There is no evidence behind Mr. Trump’s claim that Mr. Biden intervened inappropriately with Ukraine to help his son, but Democrats have been unnerved by the president’s onslaught and Mr. Biden’s halting response.
In addition to the attacks from Mr. Trump, Mr. Biden’s top rivals, Elizabeth Warren and Bernie Sanders, each out-raised him in the third quarter by about $10 million. And as Ms. Warren has emerged as Mr. Biden’s most formidable competition, Mr. Sanders, her main challenger for progressive support, just had a heart attack, casting uncertainty over whether he could siphon votes from Ms. Warren, as the Biden camp had hoped.
Even before last week, Mr. Biden’s advisers were acknowledging to donors that he may well lose both of the leadoff nominating contests in Iowa and New Hampshire.
His communications aides contend that most voters were more focused on what Mr. Trump did to prompt the impeachment inquiry than on the false claims themselves. And they pointed to the former vice president’s forceful attacks on Mr. Trump at a news conference Friday to argue that he was now ready to do battle with the president.
“This guy like all bullies is a coward,” Mr. Biden said. “He does not want to run against me.”
On Thursday, Mr. Biden, whose inner monologue rarely remains repressed, gave voice to the tension he is struggling with as he spoke at a fund-raiser in Palo Alto, Calif.
Recalling the difficulty Hillary Clinton had in confronting Mr. Trump’s campaign style, Mr. Biden worried about being “sucked into the trap of the stuff that Trump was laying. He wants you in a mud fight.”
“But when you respond to that,” he continued, “it brings you back down into that.”
Mr. Biden was even blunter, and angrier, in private after news first emerged that Mr. Trump had exhorted the Ukrainian government to investigate him and his son.
“I can’t believe this guy is going after my family like this,” he told Senator Chris Coons of Delaware, as the two campaigned in Iowa, Mr. Coons recalled.
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Leading Democrats have been pleading privately with Mr. Biden and his top aides to aggressively confront Mr. Trump, and expressing impatience with them for not seizing this opportunity to engage him in a two-man race. After all, Mr. Biden had spent months framing his candidacy as a singular crusade to oust an aberrant president.
“It’s time to really respond so everybody hears it,” said Representative Cedric Richmond of Louisiana, a campaign co-chairman. “If someone says something enough, people will start to believe it, and this president gets in his zone of telling a lie over and over again. You have to make sure people don’t believe in it.”
David Plouffe, former President Barack Obama’s campaign manager, was mystified. Mr. Biden “should use this moment and become Trump’s opponent,” Mr. Plouffe said. “I don’t understand it.”
But Mr. Biden is confronting an almost unimaginable situation: the president he hopes to challenge is facing impeachment for urging another country to help smear him. What’s more, the House inquiry centers on what Mr. Biden values most in his private and public life: protecting his family and honoring institutional norms.
Several Democrats close to Mr. Biden say he did not take on Mr. Trump sooner in large part because of his reverence for congressional prerogatives — he did not want to immediately insert himself into the House’s jurisdiction. But Mr. Biden also sought to address the attacks on his son on his own terms rather than sit for hastily arranged television interviews that would have forced him to answer questions about Hunter Biden’s work that few of his own aides dared pose.
Now, just as his monthslong lead in the primary is eroding, he faces an opponent who’s threatening his son, the political system he dedicated his adult life to and, as he approaches his 77th birthday, his last chance to become president.
Worried about his family
For Mr. Biden’s campaign, no attack could have been more difficult to deal with than one involving the candidate’s son.
Mr. Biden nearly did not run for president because of the effect it would have on his family — and particularly on Hunter Biden and his children, according to multiple advisers to the former vice president. Hunter Biden has struggled for years with substance addiction and had recently gone through a very public divorce from his first wife.
In separate interviews, Mr. Coons and his fellow senator from Delaware, Tom Carper, both said they had warned Mr. Biden that the president would target his family.
“He expected his family to be attacked,” Mr. Carper said, adding that Mr. Biden assured him he was braced for “the onslaught.’’
Mr. Biden’s family, including his son, encouraged him to enter the race, knowing the attacks were inevitable. But as Anita Dunn, one of Mr. Biden’s closest advisers, put it: “When it happens, it still feels pretty lousy.”
The Biden campaign has attempted to handle the candidate’s son with great sensitivity. Mr. Biden made clear at the outset that Hunter, a lawyer who had long advised his father on his campaigns, should not be made to feel excluded, people who spoke with him said. One adviser to Mr. Biden recently telephoned his son to solicit advice on the upcoming debate in Ohio.
But to most of Mr. Biden’s aides, Hunter Biden has been a spectral presence. He is living in Los Angeles and stayed away from Mr. Biden’s campaign launch in Philadelphia. Hunter Biden quietly attended the last two debates and appeared with his new wife, Melissa Cohen, at a July fund-raiser in Pasadena, Calif.
Still, Mr. Biden’s advisers are aware that Hunter Biden carries political vulnerabilities. His business career has intersected repeatedly with his father’s political power, through roles he had held in banking, lobbying and international finance. Working for a Ukrainian energy company beginning in 2014, he was paid as much as $50,000 a month while his father was vice president, and some of Mr. Biden’s admirers worry that, while Mr. Trump’s accusations are without merit, voters may view Hunter Biden’s actions as problematic.
In the past, Mr. Biden has bristled at questions about whether his family had benefited financially from his political career. He did so again on Friday when he was asked whether his son’s work in Ukraine represented a conflict of interest. Pointing a finger at the questioner he said: “Let’s focus on the problem. Focus on this man, what he’s doing, that no president has ever done. No president!” The Trump campaign was soon circulating a clip of the episode.
For his allies, it is both poignant and painful that Mr. Biden’s family is again at the heart of his public identity. He lost his first wife and daughter, and nearly lost his two sons, in a car accident in the weeks after he was elected to the Senate in 1972. His final years as vice president, as well as his hopes to run for president in 2016, were overwhelmed by his elder son Beau’s death from brain cancer.
Jim Mowrer, a former Democratic congressional candidate from Iowa who served with Beau Biden in the military, said he spoke to Hunter Biden early this year and got the impression he was trying to focus on personal matters rather than the campaign. Mr. Mowrer said he saw the elder Mr. Biden in Iowa last month and they discussed not Hunter but his other son, Beau.
“Beau’s death is very, very fresh in his mind, and so now these attacks on Hunter are even more unsettling,” Mr. Mowrer said.
A big bet on South Carolina
The politics of Ukraine and impeachment have been so costly for Mr. Biden, in part, because he is confronting so many other challenges in the Democratic race: a struggle to excite liberal primary voters, an ascendant rival in Ms. Warren and a decline in fund-raising that has forced him to spend even more time appealing to donors in cities hundreds of miles from the early primary states.
Mr. Biden’s campaign manager, Greg Schultz, acknowledged some of those problems in a briefing for Democratic donors at Morgan Stanley’s New York office last month. Mr. Schultz assured the group that they had a path to the nomination that depended on winning South Carolina — the fourth primary state — and then scoring big victories in the Super Tuesday primaries in March.
In South Carolina, where Mr. Biden’s support appears strongest among the early-voting states, some of his supporters are discussing a trip to Iowa before Thanksgiving — to vouch for the former vice president, and to emphasize his ability to appeal to minority constituencies, like African-Americans.
“We probably know Joe Biden a lot better than they do,” said State Senator Dick Harpootlian of South Carolina, a Biden supporter.
Mr. Schultz acknowledged at the briefing that Mr. Biden had been uneven at times during debates and on the stump. Still, he predicted Mr. Biden would maintain an advantage over Ms. Warren, saying she would struggle to overcome the persistent competition on the left from Mr. Sanders.
But Ms. Warren has recently pulled well ahead of Mr. Sanders. Now, even Mr. Biden’s own campaign aides privately acknowledge that South Carolina may not be much of a political firewall if Ms. Warren rolls through Iowa, New Hampshire and Nevada.
As he finds his way forward, Mr. Biden is relying on a circle of advisers, some formal and others less so, but there is no chief strategist. Mike Donilon, who wrote much of the Reno speech, may be the closest person to playing that role. Democrats who know Mr. Biden well say the campaign is mostly in his hands — and he makes the final calls.
While Mr. Biden’s team has done little polling in the race, he is expected to conduct a survey of Iowa Democrats next week on the Ukraine issue ahead of a new advertising push in the state.
Mr. Biden has begun to escalate his attacks on the president, and his campaign began airing a commercial hitting back at the president for trying to “pick his opponent and face only the candidates he thinks he can beat.” Still, there is no final consensus, in Mr. Biden’s camp, about how consistently he should confront Mr. Trump.
“He’s never gone negative,” said William M. Daley, the former White House chief of staff, who worked on Mr. Biden’s 1988 campaign. “That’s not him, that’s the charm of Joe.”
Thomas Kaplan contributed from Los Angeles