In the 10 days since Eric Swalwell dropped out of the race for California governor, two of his Democratic rivals’ fortunes have turned in opposite directions. Betty Yee, a former state controller, ended her campaign on Monday, while Xavier Becerra, a former California attorney general, has drawn a surge of support in multiple polls.

Mr. Becerra, whose polling numbers had languished for months, has jumped into the top tier of Democratic candidates since Mr. Swalwell’s campaign imploded amid accusations of sexual assault. Four polls in the last week have shown Mr. Becerra as receiving at least 10 percent support, at least twice what he previously had, putting him in contention in a sprawling field of candidates.

But the competition is stiff, and the race remains fluid. Mr. Becerra, who served as health and human services secretary under President Joseph R. Biden Jr., has roughly the same level of support as two other Democrats: Tom Steyer, a billionaire former hedge fund manager, and Katie Porter, a former congresswoman.

Many voters remain undecided two weeks before Californians begin receiving ballots by mail for the June 2 election. The state’s nonpartisan primary rules have added extra intrigue to the race to succeed Gov. Gavin Newsom, a Democrat who must leave office in January because of term limits. In this deeply Democratic state, no Democrat has dominated, and two Republicans — Steve Hilton, a former Fox News host who has been endorsed by President Trump, and Chad Bianco, the sheriff of Riverside County — have been among the front-runners.

In California primaries, all candidates run on the same ballot, and the two who get the most votes advance to the general election, regardless of their party. With a gubernatorial field that once included eight prominent Democrats, polls suggested that two best-known Republicans might take the top two spots because the minority party had far fewer candidates to split its votes.

Such a scenario would block Democrats from the general election and hand the governor’s office of the nation’s largest blue state to a Republican.

To prevent that possibility, Rusty Hicks, chairman of the California Democratic Party, has been encouraging Democrats to drop out if their campaigns did not seem viable. Mr. Hicks on Monday urged flagging candidates to follow Ms. Yee’s example.

“I continue to believe there are too many Democrats in the field,” Mr. Hicks said as he released the results of a poll that the California Democratic Party commissioned in an effort to thin the field.

The poll was one of four that have demonstrated momentum for Mr. Becerra since Mr. Swalwell dropped out. Mr. Becerra hired a new social media strategist last week, Tonya Lamont, Mr. Newsom’s former digital communications director, and his online presence has since boomed.

A campaign event for Mr. Becerra in Los Angeles on Saturday drew a large crowd. Mariana Salas, 45, had previously supported Mr. Swalwell but said she was looking for a new candidate and had seen social media influencers talk about Mr. Becerra in recent days.

Ms. Salas said she had identified with Mr. Becerra as a fellow Mexican American and was impressed by his experience as state attorney general.

“When he mentioned the suing of Donald Trump, I was like, ‘Oh my god, maybe this is the next guy,’” she said.

Other Democrats are also positioning themselves as the candidate who can best lead California’s fight against the Trump administration. Mr. Steyer has run on a liberal platform and received an endorsement on Monday from Our Revolution, which was founded by Senator Bernie Sanders, independent of Vermont.

It was a notable endorsement of a billionaire by a group established to fight what it calls “the billionaire class.”

Ms. Porter, a former Democratic congresswoman from Orange County, was endorsed Monday by Representative Robert Garcia, a California Democrat and a member of the Congressional Progressive Caucus. She already had support from Senator Elizabeth Warren, Democrat of Massachusetts.

Matt Mahan, the mayor of San Jose, Calif., has received millions of dollars in support from Silicon Valley executives this month.

Supporters believe that Mr. Mahan, a moderate Democrat, has an opportunity to win over former backers of Mr. Swalwell and other voters who are undecided, though he has faced criticism that he is too aligned with California billionaires, and he has not made big gains in polls over the past week.

Ms. Yee, 68, announced her withdrawal from the race in an emotional call with reporters on Monday. She had pitched herself as a budget expert who would be the scandal-free choice following Mr. Swalwell’s demise. She called herself “Boring Betty” in social media posts that highlighted her deep experience in California state government, including two terms as the state’s chief fiscal officer.

But Ms. Yee has lagged at the bottom of most polls since she entered the race in 2024 and has struggled to raise money. Her message had not broken through in a state with several expensive media markets.

“We’re living in a reality TV era,” she said in a call with reporters. “I got no gimmicks. I have no scandals.”

Orlando Mayorquín contributed reporting from Los Angeles.