When Joseph R. Biden Jr. visited San Francisco as a freshly minted senator and single father in the early 1970s, it was a well-known local fund-raiser and stay-at-home mother of five, Nancy Pelosi, who lent him her Jeep to get around town.

Over the next five decades, the two old-school Catholic Democrats who grew up in the era of Elvis Presley and were inspired by the election of the country’s first Catholic president, John F. Kennedy, cultivated a natural friendship.

They discovered that they both carried rosaries in their pockets. They learned how to wield power in Washington as leaders of top-tier congressional committees: the House Intelligence and Appropriations Committees for her, the Senate Foreign Relations and Judiciary Committees for him.

In May, at the twilights of their long careers, Mr. Biden, 81, awarded Ms. Pelosi, 84, the Presidential Medal of Freedom, anointing her the “greatest speaker of the House of Representatives in history.”

That was then. In July, Ms. Pelosi began pushing for Mr. Biden to exit the presidential race, and the two have not spoken since he made the difficult decision to step aside. There are multiple reports that Mr. Biden is angry with her. (On Wednesday, a person close to him said he was “unhappy” with the way things went.)

Ms. Pelosi has been making the rounds on a book tour, which has given her the opportunity to disparage Mr. Biden’s political team for failing, she has said, to put in place a winning presidential campaign.

It has made for an uncomfortable split screen. Ms. Pelosi, who in 2022 made the decision to step down and allow a new generation of leaders in the House to rise, is basking in her power. (“The Art of Power” is the title of her book.) Mr. Biden has all but disappeared from the stage, in part because of the role she played in stripping him of his.

It is not clear when they will speak again, a painful reality that Ms. Pelosi admits keeps her up at night. “I hope so, I pray so, I cry so. I lose sleep on it,” she told David Remnick, the editor in chief of The New Yorker, earlier this month, when pressed on whether her relationship with Mr. Biden would survive.

What she did not say is that you can’t make friends of 50 years when you are in your ninth decade, the kind who knew you way back when.

In the late 1980s, when Ms. Pelosi was first elected to Congress and was spending time in Rehoboth, Del., the beach her Baltimore-based family loved to go to when she was growing up, Mr. Biden invited her to a party to introduce her to the Democratic donor set there. There was a minor mix-up: The golfer Nancy Lopez was in the news that summer, and many of Mr. Biden’s friends thought the mystery guest he was showing around was the famous athlete. Ms. Pelosi smiled politely and did not correct them, a story she enjoys recounting.

At the 2013 mass for the installation of Pope Francis in Rome, which they attended together as part of a presidential delegation, Mr. Biden, then the vice president, and Ms. Pelosi, then the House minority leader, both received communion. Together they set off an outcry and debate within the church about whether it should have been denied to them because of their positions in favor of abortion rights.

In 2022, when Ms. Pelosi’s husband, Paul, was brutally attacked in his home, Mr. Biden was one of the first people to call her early that morning while she was still processing the news. “He was so prayerful, kind and thoughtful in his comments about Paul,” she wrote in her new book.

As she makes the rounds promoting it, Ms. Pelosi has been careful not to criticize Mr. Biden, whose legacy people close to her say she wants to burnish. “I love him so much,” she told Mr. Remnick.

“A Mount Rushmore kind of president of the United States,” she said to Lesley Stahl on CBS. “You have Teddy Roosevelt up there. And he’s wonderful. I don’t say take him down. But you can add Biden.”

She has been less generous about Mr. Biden’s staff.

“I’ve never been that impressed with his political operation,” she told Mr. Remnick. “They won the White House, bravo.” What forced her to intervene uncomfortably in his political future, she said, was that Mr. Biden’s team was “not facing the facts of what was happening.”

She has singled out one of Mr. Biden’s top gatekeepers, Mike Donilon, for particular scorn. “I didn’t even know what Donilon did,” she told The Washington Post. “I thought he was a speechwriter.” (Mr. Donilon had recently left the White House to help oversee the Biden campaign.)

And in an interview with the New York Times columnist Ezra Klein, she raised questions about whether Mr. Biden even wrote a defiant letter in early July to Democrats in Congress stating that he had no plans to drop out of the race. “It didn’t sound like Joe Biden to me,” she said, implying that a member of his staff or family may have written it for him. “It really didn’t.”

A White House spokesman, Andrew Bates, said the president’s “attention is on the future, not the past.”

Ms. Pelosi was reluctant to play the role she did in pushing Mr. Biden aside, according to people familiar with her thinking who spoke on the condition of anonymity to discuss the sensitive situation. In the interviews, she has made it clear she does not want to be the focus of the discussion. “I never called one person,” she has said repeatedly. “I never made one call.”

But people close to Ms. Pelosi said her role should have come as little surprise in that she is cleareyed and cold blooded, and will ultimately do whatever is in the best interest of the Democratic Party.

“People who know Pelosi know she is always focused on the business, and the business is ‘how do we win,’” said David Axelrod, a former top adviser to President Barack Obama. “She clearly made a judgment, she shared that judgment. It didn’t sit well with the president, understandably, and I’m sure it pains her that he feels the way he does. But I also think in her heart she knows she did the right thing for the party and the country.”

Mr. Axelrod added: “He did the right thing, and she did the right thing by urging him to do the right thing.”

It was a break from how Ms. Pelosi has conducted herself since stepping away from leadership two years ago. In her “speaker emerita” role, Ms. Pelosi has taken seriously her goal of being the “dream mother-in-law,” which she defines as offering advice only when asked and otherwise minding her own business.

Many House Democrats were shocked by her decision to stay in Congress as a rank-and-file member after decades as the Democratic Party’s House leader, and have been impressed with how she has embraced the lower-profile role. When Representative Hakeem Jeffries, Democrat of New York and the minority leader, took over, he invited Ms. Pelosi to attend the weekly leadership meeting. She declined. Instead, she is often seen sitting in the cloak room eating hot dogs with a longtime friend and confidante, Representative Anna G. Eshoo, Democrat of California. (A leadership aide disputed that account of the weekly meeting, but said Ms. Pelosi had not been involved at the leadership table since stepping down.)

Although Ms. Pelosi has told allies she was loath to insert herself into the conversation about Mr. Biden’s future, it was also clear that there are certain roles few could play.

Mr. Jeffries, still a relatively new leader, and Senator Chuck Schumer of New York, the majority leader, both had frank, one-on-one conversations with Mr. Biden about the state of the race and its concerning impact on the House and the Senate. But Ms. Pelosi could speak to Mr. Biden as a peer who had voluntarily relinquished power by stepping down from a leadership role.

Ms. Pelosi told Mr. Biden that the polls indicated he could not defeat former President Donald J. Trump in November, and that he would drag down Democrats’ chances of winning back control of the House. When he pushed back, claiming that he had seen data showing that he could win, she pressed him on what polls he was being shown. “Put Donilon on the phone,” she said, according to people familiar with the exchange. (She has denied saying that.)

The frustration with Mr. Biden’s team is not new. Ms. Pelosi’s public lashing of the team in recent days, people close to her said, reflects pent-up vexation she has harbored for some time.

There appears to be no love lost between them. Anita Dunn, a longtime adviser to Mr. Biden, seemed to take a veiled swipe at Ms. Pelosi when she recently told Politico that the task ahead for Democrats includes winning back control of the House of Representatives, “which had certain leaders in 2022 done a slightly better job, maybe we would control today, but we don’t.”

Her jab underscored how raw emotions are for the Biden team. “She’s a heat-seeking missile when it comes to winning congressional races,” Mr. Axelrod said. “You can say whatever you want about Nancy Pelosi, the one thing you can’t say is she’s not a winner.”