As rising stars in the California Democratic Party, Kamala Harris and Gavin Newsom dodged a potentially bruising campaign battle in 2015 when she chose to run for U.S. Senate and he announced his candidacy for governor.

This week, Newsom said he would avoid an even bigger potential head-to-head fight with Harris over the White House.

The California governor repeated that he would not run against Harris, standing by a comment he made last year that has new relevance after President Biden’s performance in the June presidential debate left many in the party calling for him to leave the race.

Although Biden has vowed to continue his bid for reelection, a decision Newsom has steadfastly supported, Harris and the California governor have been widely mentioned as potential replacements for the Democratic presidential nomination. As vice president, Harris appears to be the front-runner, and has the most legitimate claim given that she’s already on the 2024 ticket.

“Of course,” Newsom said when asked whether he would still decline to run against Harris. “Yes.”

If it holds, his decision could save the party and its donors from having to choose between California’s two most prominent politicians.

Declining to challenge Harris if Biden drops out places Newsom on a longer track to the White House — putting any potential presidential ambitions on hold for him until 2028 at the soonest. Harris, on the other hand, could find herself leading a last-minute rescue mission to salvage the Democratic Party’s campaign against former President Trump and to make her own presidential dreams come true.

For Newsom, averting the matchup is also a tacit acknowledgment of the political reality: Trying to skip over the vice president, and potentially the first Black female president, wouldn’t bode well for the governor, or for most other Democrats.

His own chances of becoming the Democratic nominee could also be better in four years.

“This is not the time to make that power move, and I think Gavin Newsom understands that,” said Aimee Allison, founder and president of She the People.

Allison’s group, which pushes for more women of color in elected office, advocated for Biden to select Harris as his running mate in 2020 and rallied voters to support the cause.

Back then, many expected Biden to be a one-term president. In tapping Harris, he helped revive her political career after her own presidential campaign flopped, and raised the possibility that Biden might pass the baton to her before this year’s primaries.

Though Allison commended Newsom for his recent ad campaigns in conservative states to call out their efforts to rescind reproductive rights, and for his political attacks on Florida Gov. Ron DeSantis, she said he has more work to do to introduce himself to the country.

“My sense was, and still is, that a generational transition right now with Kamala Harris heading it is logical, and it’s also the closest thing the Democrats have to winning strategy this late in the cycle,” Allison said.

Polls have shown Harris with a lead over other potential Democratic candidates. She also appears to be performing about the same as Biden has against Trump in surveys. But the longer Biden holds out, the shorter the window and the harder it will be for someone else to launch a campaign if he steps down.

At a news conference Thursday, Biden praised Harris as he vowed again to stay in the race.

“She is qualified to be president — that’s why I picked her,” he said of selecting her in 2020 as his running mate.

Newsom first said he wouldn’t run against Harris in a September interview with Chuck Todd on NBC’s “Meet the Press.” Biden had already launched his reelection campaign, but rumblings persisted about whether the president should run again. The governor made it clear that he supported Biden, and said that Harris was naturally lined up to run if the president were to step out of the race.

During a tour of swing states earlier this week to campaign for the Democratic ticket, Newsom said that as someone who has known Harris since before either of them got into politics, he believes Harris could beat Trump.

“I have no doubt about that,” he told reporters in New Hampshire. “If it comes to that. But I don’t expect it’s going to come to that.”

Harris, who was born in Oakland, spent 13 years as a prosecutor in Alameda County and San Francisco before she ran for San Francisco district attorney in 2003 and won. She went on to serve as California attorney general from 2011 to 2017, then joined the U.S. Senate.

As her contemporary, Newsom grew up in San Francisco, where he got his start as a parking commissioner in 1996. A businessman with a chain of wineries, hotels and retail shops, he was soon serving on the San Francisco Board of Supervisors, and was elected mayor in 2003. He served two terms as California’s lieutenant governor and won the 2018 governor’s race.

The governor largely avoided directly answering questions about whether he would run to replace Biden in the aftermath of the late June debate in Atlanta, which he attended as a surrogate for the president. Biden’s performance, in which he struggled to answer questions and occasionally trailed off, left Newsom facing a flurry of questions about his own ambitions as panic set in among Democrats.

But Newsom remained a soldier for the campaign, reiterating that he supported Biden as the party’s nominee. Seeking to shore up support for the president, he swatted down concerns about Biden’s mental capacity and attested to the president’s fitness based on their personal interactions.

“I think I’ve had 100 media outlets asking the same question, and I think that I’ve amply answered my support for the president, and the support I saw on the ground was demonstrable,” Newsom in a news conference at Sacramento McClellan Airport on Wednesday upon his return from the campaign trip.

Newsom also reaffirmed his stance that he would not run against Harris in a presidential campaign. Days earlier, another top Democrat, Michigan Gov. Gretchen Whitmer, had also said she wouldn’t consider running if Biden were to step down.

Forgoing a Hail Mary bid to try to become the party’s nominee at the August convention is smart politically for Newsom, said Thad Kousser, a professor of political science at UC San Diego.

Newsom can score points for unwaveringly supporting the Democratic ticket whether Biden or Harris is on top. He can continue to use the opportunity to act as a surrogate for the ticket, attending debates and traveling the country in a way that introduces him to more voters across the nation without stepping on Biden’s or Harris’ toes. Then he can wait for the dust to settle to determine his future presidential prospects.

“He took a reality and made it a virtue,” Kousser said. “Certainly, he gave up a short-term possibility of coming into this role and leading the Democrats to victory in 2024. He set himself up quite well for 2028 and beyond.”

If Harris or Biden wins in November, Harris would be a front-runner again in the 2028 presidential contest, which would leave Newsom in a tough position if he wants to run then. A Democratic loss in November could bring Harris’ presidential hopes down with the campaign and open the door for Newsom, or someone else, to grab the nomination in four years.

Such a loss would mean Newsom’s last two years in the governor’s office would be spent in a high-profile battle with an antagonistic Trump White House, which could set the stage for a 2028 campaign in which his top California competition is already neutralized.

“If Joe Biden, or another Democrat loses, I think Gavin Newsom is the presumptive leader of the opposition against Donald Trump,” Kousser said, “because he has been the most forceful critic of the direction that Donald Trump wants to take America.”

Times staff writer Seema Mehta contributed to this report.