Multiple times each day, President Biden dials up Mike Donilon, a close adviser since the 1980s, to chew on the latest polls and headlines.

“What’s your instinct? What do you think?” Mr. Biden will ask Mr. Donilon, who recently left the White House for the campaign’s Delaware headquarters.

Once a week, Mr. Biden summons Ron Klain, his former chief of staff, to workshop the best attacks to use against former President Donald J. Trump as the presidential debate draws closer.

When he leaves for Delaware on weekends, Mr. Biden seeks out Ted Kaufman, a confidant who represents the president’s ties to the state that introduced him to the national stage more than a half-century ago. It was Mr. Kaufman who was brutally direct with Mr. Biden when a plagiarism scandal threatened his first campaign for president in 1987.

“There’s only one way to stop the sharks,” Mr. Kaufman told him at the time, “and that’s pull out.” Mr. Biden did.

Interviews with dozens of people close to the president reveal a truth at the heart of Mr. Biden’s political life: While he is surrounded by a diverse and multigenerational crowd of campaign operatives, policy experts and cabinet secretaries, he reserves his full trust for a small circle of insiders who are the definition of old school.

The three are at the center of the Biden world, part of an echo chamber where dissent is rare. In important moments, each has told the president news he did not want to hear, although not one of them said no when the president was considering whether to run for a second term. They are also decades older than the young voters who could decide the election, which worries many of the president’s allies.

Mr. Klain is the youngest at 62. Mr. Donilon is 65. Mr. Kaufman is 85, four years older than Mr. Biden. Each has earned the president’s trust over not just years but decades. On this last of Mr. Biden’s four presidential campaigns, the three are his political comfort animals on speed dial.

“They not only have Biden’s trust but they have the trust of everyone who matters most to him,” meaning the president’s family members and particularly Jill Biden, the first lady, said Michael LaRosa, a former East Wing press secretary and special assistant to Mr. Biden. “It is very rare that you have the trust, respect and confidence from both of them. That’s a very uncommon level of dependency all three men possess in that orbit.”

They have been with Mr. Biden through some of the worst moments: Two aneurysms. His time as Senate Judiciary Committee chairman during the fight over the Supreme Court nomination of Robert H. Bork. The withering criticism he faced after his aggressive questioning of Anita Hill in the hearings for Clarence Thomas’s nomination. The death of Mr. Biden’s son Beau.

“They all share a layer of scar tissue in common with both Bidens that few others can understand,” Mr. LaRosa said.

Mr. Donilon and Mr. Klain have traveled to Camp David in recent days to help prepare Mr. Biden for his debate on Thursday in Atlanta with Mr. Trump. They are joining a rotating cast of aides — including Jeff Zients, the White House chief of staff, and Jen O’Malley Dillon, who runs the campaign — visiting the retreat.

(The part of Mr. Trump will be played in practice sessions by Bob Bauer, the president’s personal attorney.)

Mr. Kaufman is not expected to be at Camp David but is never out of reach when Mr. Biden needs gut-checks and support.

“It’s not like he needs to figure out what he believes on a subject,” said Mark Gitenstein, the ambassador to the European Union who first worked as a lawyer for Mr. Biden more than four decades ago. “It’s: ‘If I make this argument, does this work? Or should I try this argument?’”

Mr. Klain, the president’s whisperer with progressives and viewed as an expert at wielding the levers of government, managed the 2022 nomination of Ketanji Brown Jackson to the Supreme Court. Mr. Donilon, said to channel Mr. Biden’s voice as well as the president himself, is the architect of the campaign’s theme that democracy is at stake if Mr. Trump wins. Mr. Kaufman is basically kin: In 1972, he was standing with Mr. Biden’s family at the Hotel du Pont on the night of his first Senate victory.

All three declined to comment for this article.

“President Biden values diverse points of view and is proud of his full team of advisers, including recent arrivals and longtime aides,” said Andrew Bates, a White House spokesman.

Still, a former adviser said Biden’s tight circle frustrates everyone outside of it.

“Having advisers that are close friends and refusing to listen to others is the kiss of death,” said John Kasich, a former Republican governor of Ohio who endorsed Mr. Biden at the 2020 Democratic convention.

“They absolutely have been too insular in the way they do things, and I think there’s probably been a deliberate effort to keep dissonant voices out,” he said. “When your circle’s too small, you know, it’s a disadvantage in anything you do.”

Mr. Biden has an answer for them. “I was working on this,” the president will say with a smile, “before you were born.”

The Strategist

At the end of April, Ron Klain confidently told a cable TV host: “I think there will be debates.”

Two weeks later, the president formally challenged Mr. Trump to two debates, setting out conditions that precisely matched the ones Mr. Klain had outlined publicly on the MSNBC program. It was no coincidence.

Mr. Klain no longer occupies the big office down the hall from the Oval. But the two men continue to talk nearly every day. The calls and visits are, more often than not, instigated by the president, who leans on Mr. Klain for short-term tactical advice and longer-term strategy.

Last month, Mr. Klain said he would take time off from his job as chief legal officer at Airbnb to help prepare Mr. Biden for the two debates with Mr. Trump. Several Biden advisers said that Mr. Klain is able to redirect Mr. Biden when he meanders, a prized skill when the work involves cutting the loquacious president’s remarks into debate-sized sound bites.

“That’s a really good point, sir,” Mr. Klain will say, before guiding the president back to the original point. Mr. Klain, whom Republicans sometimes referred to as Mr. Biden’s “prime minister,” is the author of 21 debate rules for candidates. No. 10: “Punches are good, counterpunches are better.”

In debate preparations, Mr. Klain is known to replay videotapes of Mr. Biden’s past debates, focusing on slip-ups or responses that ran on for too long. Mr. Biden, who is not used to taking blunt criticism from anyone, then incorporates Mr. Klain’s feedback into his next practice round, according to a longtime Democratic operative who has seen the pair work together.

Mr. Klain’s presence in the president’s orbit is a testament to their relationship — not quite son and father, but more than staffer and boss. Born and raised in Indianapolis, Mr. Klain was still a law student at Harvard when he first worked for Mr. Biden in the Senate 38 years ago, eventually rising to become chief counsel on Mr. Biden’s Judiciary Committee.

But he was not always by Mr. Biden’s side.

Mr. Klain was briefly chief of staff for Vice President Al Gore and oversaw the recount effort in Florida in 2000. (He was later portrayed in a movie by Kevin Spacey.) He was involved in John Kerry’s 2004 campaign and spent some years as an adviser to Steve Case, a founder of AOL.

Mr. Biden’s trust was tested in 2015 when Mr. Klain went to work for Hillary Clinton as she pursued the presidency, signing on before Mr. Biden had formally decided against a run of his own. “I am definitely dead to them,” Mr. Klain later fretted to a colleague in an email that was part of a trove of documents revealed by WikiLeaks.

But Mr. Klain eventually returned to the center of the president’s universe as his first White House chief of staff, over the initial reservations of a still-skeptical Jill Biden, according to people familiar with the decision.

Behind the scenes, he drafted Democratic talking points that excoriated Senator Joe Manchin of West Virginia for pulling his support for the president’s economic plan, but later made up with him over a pork roast at the home of Commerce Secretary Gina Raimondo.

Long hours in the West Wing, an ailing mother and too many greasy hamburgers from the Navy mess forced Mr. Klain to make a tearful exit in early 2023. On his final day in the White House, Mr. Klain broke down in tears as he said: “This is the best job I’ve ever had.”

The Guru

Shortly after Mr. Donilon decamped from the White House in January to help oversee Mr. Biden’s campaign from Delaware, he reached out to allies, asking for advice. The White House creates a bubble around its occupants — a former adviser to President Barack Obama described it as like working within a “submarine” — and Mr. Donilon wanted a view from outside.

“Tell me what I need to know,” Representative Debbie Dingell, Democrat of Michigan, recalled Mr. Donilon asking her at a party. “I need you to tell me the truth.” Ms. Dingell would only say that she told Mr. Donilon that “Michigan is a purple state,” and that the campaign should operate accordingly.

It often falls to Mr. Donilon to deliver the news of polls that show the president struggling, or more recent ones that suggest some improvement. And it is Mr. Donilon — more than anyone else — who helps Mr. Biden frame his actions in a way that supports the longstanding Biden narrative.

In 2020, he devised the winning strategy for the president’s campaign against Mr. Trump: focus on the threat to democracy, he told Mr. Biden.

“In my view, every presidential campaign is won or lost with the very first decision you make, which is, what is it about?” Mr. Donilon said at a forum at the Harvard Kennedy School after the election. “Why are you doing it? And the problem that most campaigns have is they never reach, with any clarity, an answer to that question.”

Understated, with a shock of white hair and bushy eyebrows, Mr. Donilon is viewed as a sphinx by his more talkative colleagues, sitting silently during conversations with the president. But few aides command the president’s attention as fully as Mr. Donilon.

In his book, “Promise Me, Dad,” Mr. Biden recalled the night of Oct. 20, 2015, as the small circle of friends and family met to decide whether he would run for president that year. Mr. Donilon sat quietly looking at Mr. Biden as he considered the idea of a run just months after the death of Beau.

“I caught him looking at me and gestured, What is it, Mike?” Mr. Biden wrote. “‘I don’t think you should do this,’ he said.” Mr. Biden decided against running that year, waiting another four years to challenge Mr. Trump.

The three longtime advisers may be of a generation long before social media, but Democrats say Mr. Biden’s campaign runs like a sophisticated presidential re-election machine should: Operatives pore over polling and voter micro-data, target crucial communities in the swing states and aggressively use social media to reintroduce Mr. Biden to younger Americans.

Yet Mr. Donilon is consulted on virtually every major decision. He is often joined by other longtime aides, including Anita Dunn, who oversees communications strategy, and Steve Ricchetti, who manages relationships on Capitol Hill. The president also leans on Bruce Reed for policy advice. Ms. Dunn, Mr. Ricchetti and Mr. Reed have been with Mr. Biden for years, but have not clocked the same mileage with the president as the core counselors.

Mr. Donilon may be the closest thing that Mr. Biden has to an alter ego — someone who can divine what the president is thinking and translate it into a political message. It was Mr. Donilon who guided Mr. Biden through his public response after the Supreme Court struck down Roe v. Wade in 2022. Mr. Donilon, aware that the Irish Catholic president was uncomfortable talking about abortion, framed the issue in Mr. Biden’s speeches as a matter of personal freedom and privacy.

His value, people who know Mr. Biden say, is understanding how the president would want to address an issue before it ever reaches the Oval Office.

The Confidant

In early January this year, Mr. Biden and Mr. Kaufman spent almost two hours at the Fieldstone Golf Club Grille in Wilmington, not far from the president’s home away from the White House.

There are few moments in Mr. Biden’s political and personal life that the two haven’t shared, and little they don’t discuss. Mr. Kaufman, who has a fast-talking, blunt style, is less forthcoming about the details of their meetings.

“It’s my policy to not talk about my discussions with the president,” he often says.

Mr. Kaufman, a Philadelphia native who lives in Wilmington full time now, has been ever-present. Starting in the earliest days of Mr. Biden’s political career, he has made appearances including a seemingly endless string of local Democratic fund-raisers around the country. Mr. Kaufman, who was Mr. Biden’s longtime Senate chief of staff, is one of the handful of advisers frequently at Mr. Biden’s Wilmington home.

When Mr. Biden took the Amtrak back and forth from Washington to Wilmington every day, Mr. Kaufman was often in the seat next to him. (His advice: If you don’t know the answer to one question when you brief him, that’s the question he will ask.) And Mr. Kaufman filled in as Delaware’s senator when Mr. Biden became vice president.

He has been entrusted with some of the most sensitive decisions Mr. Biden has made over the course of his career. In 1986, it was Mr. Kaufman who helped him quietly construct the blueprint for his first run for the presidency. “We’re just trying this out,” Mr. Biden would say.

More than 20 years later, Mr. Kaufman, fully aware of the scars of that race, was the only non-Biden in the room when Mr. Biden’s family sat him down and asked him to run again in 2008.

For the president, the lunches are more than just a moment to catch up with an old friend. He seeks out Mr. Kaufman to get insight from — and trade gripes with — a confidant whose instincts have always leaned toward protecting the Biden political brand. In 2020, it was Mr. Kaufman who managed Mr. Biden’s transition into the office he had sought for decades.

“Joe has long since said that Ted Kaufman is the wisest man he’s ever known,” Valerie Biden Owens, the president’s sister, wrote in her memoir. “Ted is his true north.”

Kate Bedingfield, who was a top communications adviser for Mr. Biden for years and is now a political commentator on CNN, said the three men are uniquely able to keep “the essence of Joe Biden” at the center of everything.

“Everyone understands and appreciates that when they speak for the president, they are channeling his voice in full,” she said. “Because very few people without the last name Biden know him better than those three.”