Governor Gavin Newsom of California is defending himself against a charge that he brushed off a phone call from Vice President Harris in the hours after President Biden dropped out of the 2024 presidential race.

The charge appears in Ms. Harris’ new campaign memoir, “107 Days,” which reports say netted her upwards of $20 million and which details her’ frantic efforts to contact prominent Democrats in the hours following Mr. Biden’s sudden withdrawal from the race.

Describing her effort to reach Mr. Newsom, Ms. Harris wrote in her notes: “Hiking. Will call back.” She adds, in a pointed parenthetical observation: “He never did.”

Responding to the vice president’s account on Friday, Ms. Newsom told reporters he had not recognized Ms. Harris’ phone number when she called. “There was an unknown number,” he said. “Meanwhile, I was on a text chain, trying to get in touch with the Biden administration, because I was completely surprised that the president dropped out.”

Mr. Newsom, who endorsed Ms. Harris within hours of Mr. Biden’s announcement, called the episode “trivial” but insisted he had been working on his endorsement statement when Ms. Harris called – a fact not mentioned in the book. “That exact same moment, was working with my team to draft a statement.”

Mr. Newsom and Ms. Harris, who both launched their careers in San Francisco in the late 1990s and early 2000s, are considered among the prospective front-runners for the Democratic Party presidential nomination for 2028.

Ms. Harris’ memoir also recounts a chilly encounter between her husband, Doug Emhoff, and first lady Jill Biden at a Fourth of July White House celebration, just weeks before Mr. Biden’s withdrawal.

According to Ms. Harris, Jill Biden pulled Mr. Emhoff aside to the White House’s Blue Room for a private conversation. She appeared “tense, even angry,” Ms. Harris writes in the book, set to be released Tuesday.

“What’s going on?” Ms. Biden reportedly asked. “Are you supporting us?”

Shocked by the implication of disloyalty, Mr. Emhoff replied, “Of course we are supporting you,” according to the memoir.

“Okay. That’s really important. We need to know that,” Ms. Biden snapped back.

Ms. Harris noted that her husband was visibly upset after the exchange, frustrated that the first lady doubted the second couple’s loyalty to the Bidens.

After Mr. Biden officially dropped out and Ms. Harris became the Democratic nominee, Jill Biden reportedly issued another warning to Mr. Emhoff during a phone call: “Be careful what you wish for. You’re about to see how horrible the world is.”

Ms. Harris attributes Jill Biden’s hostility to lingering resentment from the 2020 primary campaign, when Ms. Harris aggressively challenged Mr. Biden over his early opposition to school busing. “I suspect Jill hadn’t quite forgiven me for the 2019 primary debate, when I’d gone hard at Joe over his early opposition to busing,” Ms. Harris wrote.

The memoir reveals that Transportation Secretary Pete Buttigieg was Ms. Harris’ preferred choice for running mate, but she ultimately decided against selecting him. Despite his qualifications, Ms. Harris concluded it was “too big of a risk” to choose Ms. Buttigieg, who is openly gay, while already asking voters to accept a black woman as president.

Ms. Harris also considered Governor Josh Shapiro of Pennsylvania but had “a nagging concern that he would be unable to settle for a role as number two and that it would wear on our partnership.” Several reports at the time said Mr. Shapiro opted out of accepting the veep slot, fearing Ms. Harris was destined to lose.

She ultimately selected Governor Tim Walz of Minnesota, though his debate performance against J.D. Vance left her frustrated. “You’re not there to make friends with the guy who is attacking your running mate,” she said while watching the debate.

The book also details Ms. Harris’ own campaign mistakes, including a damaging appearance on “The View” where she failed to differentiate herself from Mr. Biden’s record. When asked what she would have done differently than Mr. Biden, Ms. Harris blanked and said, “There is not a thing that comes to mind.”

“I had no idea I’d just pulled the pin on a hand grenade,” Ms. Harris writes, noting that her staff were “besides themselves” about the “gift to the Trump campaign.”

Ms. Harris also writes that Mr. Biden initially planned to wait a day before endorsing her as his successor, an idea she strongly opposed. “If you want to put me in the strongest position, you have to endorse me now,” she recalled telling him. Mr. Biden ultimately endorsed her shortly after announcing his withdrawal.