President Trump is gearing up to launch blistering personal attacks on Joe Biden and his family in the first presidential debate on Tuesday, while Biden is bracing for an onslaught and worried allies are warning the Democratic nominee not to lose his temper and lash out, according to people with knowledge of the strategies in both camps.

Trump has told associates he wants to talk specifically about his opponent’s son Hunter Biden and mused that the debates are when “people will finally realize Biden is just not there,” according to one adviser. The president is so eager to lay into his rival that he has called aides to test out various attacks, focusing on broadsides that cast Biden as a longtime Washington insider with a limited record of accomplishment, said another adviser, who like many interviewed for this story spoke on the condition of anonymity to candidly describe private talks.

Biden and his advisers are anticipating a venomous barrage, according to a person with knowledge of their thinking, and they are preparing to counter with an affirmative case for a Biden presidency. The Democrat wants to stay focused on how he would address the coronavirus pandemic and the country’s economic problems, which he blames Trump for worsening.

The prospect of a cage match between a president for whom no subject is off-limits and a challenger who can be openly emotional is making some Biden advisers nervous. They see a fine line between Biden’s passion and empathy, which can appeal to voters, and the raw anger that sometimes gets him in trouble and could undercut his pitch as a calming alternative to a president who thrives on chaos.

“When you go at his family, he becomes hotter than hell, which is part of the thing I worry about,” said John Morgan, a Florida trial lawyer and major Biden donor. “I think what Biden has to be careful about is not letting his Irish temper blow when that happens.”

Biden’s emotion, especially when it comes to his family, has often been a strong suit. But he has also shown a tendency to lose his composure when his record, and especially his decency, are questioned — such as when he declared in an interview with “The Breakfast Club” that African Americans considering voting for Trump “ain’t black,” or when he snapped, “Why, why, why, why, why?” at a reporter who asked during the primary why he had attacked a rival.

Trump’s deficit in the polls arguably means there is more pressure on him than Biden to score a big win, and his supporters are voicing their own worries. The president’s repeated mocking of Biden as incoherent could make it easy for the challenger to exceed expectations, Trump’s allies say, and they concede the president is always capable of sabotaging his own message.

Trump has shown little interest in studious preparation, but he is expected to meet with advisers this weekend to talk about the debate. “The president’s view is: He’s been president for four years, he’s been in training every day,” one ally said. “He thinks he doesn’t need any prep.”

Still, there are reasons for Democrats’ apprehension about their 77-year-old nominee, who last ran for office in 2012. In recent months, Biden has largely been cloistered away from hostile settings, and some supporters fret that he might be rusty when he confronts what could be some of the most vicious criticism he’s ever faced in person.

“It’s like training for a knife fight and somebody is getting an Uzi,” lamented one Democratic congressional aide.

Biden’s friends and advisers are urging him not to get dragged into ugly exchanges. “There is an old saying in debate circles: When you get down in the mud and wrestle with a pig, the pig has fun and you get covered in mud,” said Sen. Christopher A. Coons (D-Del.), a close Biden confidant. “And the word that is typically used is not ‘mud.’ ”

Biden himself has expressed a similar concern. “I hope I don’t get baited into getting into a brawl with this guy,” he said at a virtual fundraiser this month. He added, “It’s going to be hard, because I predict he’s going to be shouting” and interrupting.

Biden did engage in a series of debates during the primary, sometimes taking hard shots from his rivals, including his now running mate, Sen. Kamala D. Harris (D-Calif.).

Biden will try to speak directly to the voters, the person with knowledge of his team’s thinking said, and will correct Trump when merited. But Biden’s advisers believe strongly that he should not get bogged down in fact-checking the president, leaving that mostly to moderator Chris Wallace.

Biden and his aides are expected to hunker down in preparation for the debate in coming days, according to a person with knowledge of the plans. Former White House counsel Bob Bauer is standing in for Trump, according to a person with knowledge of the situation. Bauer did not immediately respond to a request for comment.

For all their emphasis on telling their own story, there is no doubt Trump is squarely on the minds of Biden’s aides and allies. Philippe Reines, who portrayed Trump in Hillary Clinton’s mock debates four years ago, said he recently gave Ron Klain, who is playing a leading role in Biden’s preparation, his “Trump uniform” — the baggy blue suit, cuff links and lift dress shoes he wore to get in character.

“He laughed,” Reines said of Klain’s reaction, adding that Klain told him, “We’ll make good use of it.” (Klain said he was joking and the team is not using the outfit.)

But the lessons from Clinton’s experience four years ago are murky. She was widely considered the winner of all three debates with Trump, yet in the end it was not enough to avoid defeat.

And Trump has shown he considers few tactics off-limits. In one 2016 primary debate, he boasted about the size of his genitalia. In a debate with Clinton, he brought a group of women who had accused her husband of sexual misconduct, though he was not allowed to seat them in the gallery.

Tuesday’s debate — the first of three between Trump and Biden — will culminate weeks of vitriol. Trump has accused Biden of taking performance-enhancing drugs and questioned his mental acuity, without any evidence. Biden has mocked Trump for walking unsteadily down a ramp, flashed visible anger over his opponent reportedly insulting fallen soldiers and argued that Trump’s response to the pandemic disqualifies him from the presidency.

Adding to the tension is a heated battle over the Supreme Court, with Trump moving swiftly to fill the vacancy created by the death of liberal justice Ruth Bader Ginsburg. The three debates — along with one between Harris and Vice President Pence — will probably unfold at the same time as a ferociously bitter confirmation process that could determine the court’s leaning for decades.

It all kicks off over 90 minutes on Tuesday night on the Health Education Campus of Case Western Reserve University and the Cleveland Clinic. Trump and Biden will be at podiums a safe distance apart, as specified by health guidelines, according to Frank Fahrenkopf, co-chair of the Commission on Presidential Debates. From the start, the candidates will confront unprecedented decisions, such as how or even whether to greet each other at a time when medical experts are warning Americans not to shake hands.

Biden advisers feel that the presidential race is being driven largely by Trump’s widely criticized response to the pandemic, which has cost more than 200,000 U.S. lives, and that the debate is unlikely to alter that dynamic, according to the person with knowledge of their thinking. With the president trailing, a series of poor debate performances could “put a nail in the coffin” of Trump’s chances, argued one Biden adviser.

Some of Trump’s advisers say he has not been as focused on the debate as they would like. The process at times reminds them of 2016, when they would try to prepare Trump and he would get distracted and tell stories, according to one adviser.

Trump is not undergoing traditional debate preparation with someone playing Biden, according to officials with knowledge of his strategy; rather, he’s relying on a familiar coterie of friends and strategists. Former New Jersey governor Chris Christie has taken on a prominent role in advising Trump on the debate, while senior campaign adviser Jason Miller has watched old clips of Biden and analyzed them.

Former New York mayor Rudolph W. Giuliani is also involved, and others involved in the discussions include top advisers Jared Kushner and Hope Hicks, officials said. Trump is likely to focus on attacks about Biden’s handling of China while in office, along with the former vice president’s comments on the coronavirus from the early part of the pandemic. He is likely to accuse Biden of being too beholden to more liberal figures in the Democratic Party, advisers say.

Aides have sought to persuade Trump for weeks to stop lowering expectations for Biden’s performance. “We take Joe Biden very seriously,” said Trump campaign spokesman Tim Murtaugh. “He’s had decades in the Senate where all he does is debate.”

Yet Trump routinely seeks to cast the former vice president as frail, ineffective and captive to his party’s left wing. “Biden doesn’t know he’s alive,” the president said this month.

That worries some of the president’s allies. “The bar for Biden is very low. The expectations are low. So he doesn’t have to do much to come out looking good,” said Newsmax Chairman Christopher Ruddy, a close friend of Trump’s. “The president just goes out there and says whatever is on his mind. It could get pretty wild.”

One topic Trump is eager to broach is Hunter Biden. “I think it will be brought up in the debate,” Trump said at a recent rally in Fayetteville, N.C., shouting, “Where is Hunter?”

Hunter Biden has long been a focus of Trump and his allies, because he served on the board of a Ukrainian energy company while his father was coordinating the Obama administration’s Ukraine policy. Neither has been accused of wrongdoing. Trump was impeached for pressuring Ukraine to investigate the Bidens, but the Senate acquitted him.

Biden campaign spokesman Andrew Bates hit back at the prospect that Trump would go after Hunter Biden during the debate. “For Donald Trump to demonstrate that the only case he can make for himself is to lash out at Joe Biden’s children would be the ultimate admission that his presidency is a weak, pathetic failure,” Bates said.

Few if any topics irk Biden as much as attacks on his family. When a voter in Iowa accused him of sending Hunter to Ukraine and “selling access to the president,” Biden responded sharply: “You’re a damn liar, man. That’s not true.” There was no evidence for the man’s claim.

Biden later challenged the man — who also voiced worries about Biden’s age — to do push-ups with him or take an IQ test, suggesting how he can be knocked off course by attacks that have a personal edge.

On Tuesday, supporters are hoping Biden will appear poised and presidential — an area where many Democrats believe he fell short in the primary debates, awkwardly cutting himself off and memorably botching instructions on how to text his campaign.

“He’s an uneven debate performer,” said veteran Democratic strategist Donna Brazile. “When you think Joe Biden, you don’t think, ‘Well, you know, he’s the king of the kings.’”

In addition to Klain, the preeminent Democratic debate coach, longtime Biden adviser Mike Donilon is also involved in debate preparations, as is senior adviser Anita Dunn, according to people with knowledge of the preparations.

Biden is an experienced debater, and some supporters say he does best in one-on-one meetings, citing his performance in vice-presidential matchups against Sarah Palin in 2008 and Paul D. Ryan in 2012.

But his associates and allies agree that Trump is unlike any opponent he has faced.

Sen. Chris Van Hollen (D-Md.), who portrayed Ryan in Biden’s 2012 practice debates, said their sessions focused largely on policy, as Ryan had a reputation as a wonk on budget issues.

“That’s a totally different ballgame,” he said.

Jacqueline Alemany contributed to this report.