PHOENIX — Joe Biden’s time in public office is now behind him, but his age and mental acuity have become a litmus test for the next leaders in his party.

A new book that alleges White House aides covered up Biden’s physical and mental decline has put the questions about Biden’s health back in the spotlight, months after former Vice President Kamala Harris lost to President Donald Trump. Several potential Democratic contenders for the 2028 nomination in recent days have been asked whether they believe Biden was declining in office or whether he should have sought reelection before a disastrous debate performance led to his withdrawal.

Many Democrats would prefer to focus on Trump’s second term. Trump has done his best to prevent that — mentioning Biden’s name an average of six times per day during his first 100 days in office, according to an NBC News analysis — and Republicans have followed his lead, betting that voters frustrated by Trump’s policy moves will still prefer him over memories of an unpopular presidency.

In the race for Virginia governor, one of this year’s highest-profile contests, Republican Winsome Earle-Sears is running a pair of television ads tying Democrat Abigail Spanberger to Biden, with images of the two hugging and the former president calling her a friend.

“The stench of Joe Biden still lingers on the Democratic Party,” Democratic strategist Sawyer Hackett said. “We have to do the hard work of fixing that, and I think that includes telling the truth, frankly, about when we were wrong.”

Democratic Sen. Chris Murphy of Connecticut told Politico this week that “there’s no doubt” that Biden, now 82, experienced cognitive decline as president.

Pete Buttigieg, the former transportation secretary, wasn’t nearly as blunt but still stopped short of defending Biden’s decision to run. He responded “maybe” when asked Tuesday whether the Democratic Party would have been better off if Biden hadn’t tried to run for a second term.

“Right now, with the advantage of hindsight, I think most people would agree that that’s the case,” Buttigieg told reporters during a stop in Iowa.

Illinois Gov. JB Pritzker said he didn’t see signs of mental or physical decline in his meetings with Biden.

“I saw him a few times,” he told CNN this week. “I certainly went to the White House whenever there was an opportunity for me to make the case for something for people in my state. And I never had the experience of anything other than a guy who brought to the table a lot of good ideas about how to solve problems.”

The book “Original Sin,” by journalists Jake Tapper of CNN and Alex Thompson of Axios, revives a core controversy of Biden’s presidency: his decision to run for a second term despite voters, including Democrats, telling pollsters that he should not run again. Biden would have been 86 at the end of a second term had he won in November.

A spokesperson for Biden did not respond to a request for comment.

“We continue to await anything that shows where Joe Biden had to make a presidential decision or where national security was threatened or where he was unable to do his job,” the spokesperson has told many media outlets in response to the book.

Even as Democratic leaders dismissed both a series of verbal flubs and Republican allegations about his declining acuity, Biden faced widespread doubts within his own party.

In January 2022, just a year into Biden’s first term, an AP-NORC Center for Public Affairs Research poll found that only 48% of Democrats wanted him to seek reelection. That fell to 37% of Democrats in an AP-NORC poll conducted in February 2023. Three-quarters of Americans — and 69% of Democrats — said in August 2023 that they believed Biden was too old to serve as president for another four-year term.

And shortly after his debate flop, nearly two-thirds of Democrats said Biden should withdraw from the race.

Biden and former first lady Jill Biden appeared on ABC’s “The View” in a preemptive defense of his health and decision-making before the first excerpts of “Original Sin” were published.

He said he’s responsible for Trump’s victory but attributed Harris’ loss, at least in part, to sexism and racism. He maintained that he would have won had he remained the Democratic nominee. Both Bidens rejected concerns about his cognitive decline.

Patricia McEnerney, a 74-year-old Democrat in Goodyear, Arizona, said Biden should not have tried to run again.

“I think it’s sad the way it ended,” she said.

She compared him to Douglas MacArthur, the World War II and Korean War general famously dismissed by President Harry Truman.

“I think he needs to stop giving interviews. I think that would help,” McEnerney said. “Like MacArthur said, generals just fade away.”

Janet Stumps, a 66-year-old Democrat also from Goodyear, a Phoenix suburb, had a different view.

“I don’t think it’s going to hurt the Democrats,” Stumps said. “I feel badly that he feels he has to defend himself. I don’t think he has to. Everybody ages. And the fact that he did what he did at his age, I think he should be commended for it.”

Hackett, the Democratic strategist, predicted Biden won’t be a major factor in the 2026 midterms or the 2028 presidential primaries. But he said Democrats who want voters to trust them would be well-served “by telling the truth about the mistakes that our party made in the run-up to 2024.”

“Those mistakes were largely driven by Joe Biden, and I think any Democrat not willing to say that is not really prepared to face the voters, who want the truth and they want authenticity,” Hackett said.

Rick Wilson, a former GOP strategist who co-founded the anti-Trump group the Lincoln Project, said Republicans want to talk about Biden to avoid defending Trump. But he said the strategy is folly.

Besides “political nerds,” he said, “no one else cares.”

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Associated Press writer Thomas Beaumont contributed to this report from Cedar Rapids, Iowa.