In her upcoming book about her disastrous 2024 run for the White House, Vice President Kamala Harris says President Biden’s decision to seek re-election was fundamentally misguided, according to excerpts published Wednesday.

In “107 Days,” set to hit bookstore shelves on September 23, Ms. Harris offers a candid assessment of the political calculations that led to Mr. Biden’s ill-fated 2024 campaign, ultimately characterizing the decision-making process as “recklessness” rather than political wisdom.

Ms. Harris writes that the White House’s approach to Mr. Biden’s re-election bid was driven more by personal loyalty than strategic thinking. She describes how administration officials repeatedly deferred to the president’s personal wishes rather than making hard political calculations about his electability.

“‘It’s Joe and Jill’s decision.’ We all said that, like a mantra, as if we’d all been hypnotized. Was it grace, or was it recklessness?” Ms. Harris writes. “In retrospect, I think it was recklessness. The stakes were simply too high. This wasn’t a choice that should have been left to an individual’s ego, an individual’s ambition. It should have been more than a personal decision.”

The former vice president said her position within the administration made it difficult when it came to addressing Mr. Biden’s electoral prospects.

Of all the people in the White House, Ms. Harris says. “I was in the worst position to make the case that he should drop out. I knew it would come off to him as incredibly self-serving if I advised him not to run. He would see it as naked ambition, perhaps as poisonous disloyalty, even if my only message was: Don’t let the other guy win.”

Despite her criticism of the decision-making process, Ms. Harris defended Mr. Biden’s mental capacity and leadership abilities throughout the excerpts published Wednesday. She pushes back against suggestions that the administration was covering up the president’s cognitive decline.

“Many people want to spin up a narrative of some big conspiracy at the White House to hide Joe Biden’s infirmity. Here is the truth as I lived it,” she writes. “Joe Biden was a smart guy with long experience and deep conviction, able to discharge the duties of president.”

However, Ms. Harris does acknowledge that age became a factor in Mr. Biden’s performance, particularly during high-pressure moments like his disastrous June debate against Mr. Trump.

“On his worst day, he was more deeply knowledgeable, more capable of exercising judgment, and far more compassionate than Donald Trump on his best. But at 81, Joe got tired,” she writes. Yet she attributes Mr. Biden’s poor debate performance to an exhausting schedule rather than cognitive issues.

“I don’t think it’s any surprise that the debate debacle happened right after two back-to-back trips to Europe and a flight to the West Coast for a Hollywood fundraiser,” Ms. Harris writes. “I don’t believe it was incapacity. If I believed that, I would have said so. As loyal as I am to President Biden, I am more loyal to my country.”

The memoir also discloses friction between Ms. Harris and Mr. Biden’s inner circle, particularly regarding how the White House handled attacks on her performance as vice president. She writes that Mr. Biden’s communications team failed to adequately defend her against Republican and conservative media criticism, despite having extensive resources at their disposal.

“They had a huge comms team; they had Karine Jean-Pierre briefing in the pressroom every day,” she writes. “But getting anything positive said about my work or any defense against untrue attacks was almost impossible.”

According to Ms. Harris, this reluctance to defend her became more pronounced as her polling numbers improved while Mr. Biden’s declined. “They didn’t like the contrast that was emerging,” she writes.

“107 Days” chronicles the brief period between Mr. Biden’s withdrawal from the 2024 race and Mr. Trump’s eventual election victory. Ms. Harris’s campaign, lasting just 107 days, was the shortest presidential campaign in modern American history.