Jones led Thompson by roughly 5 percentage points with 95% of votes counted, according to the AP. The call came more than a week after Election Day, as the challenger maintained a narrow but steady advantage.

"It wasn't a partisan mandate," Jones told reporters. "It was really just, 'Government is not working for us. It's too corrupt, it's bought out.'"

Jones, 35, is already in Washington for freshman congressional orientation. He said his early priorities will include anti-corruption measures targeting corporate money and stock trading by members of Congress, as well as protecting health care.

"You'll see a lot of focus out the gate on corruption," he said. "I think you're going to see a lot of movement out the gate on healthcare and really making sure that the [H.R. 1 Medicaid] cuts we saw do not become permanent realities for our country."

The race unfolded in a newly redrawn district that stretches from the Napa Valley to the Sacramento suburbs and rural areas in the north. Nearly half of District 4 is new territory after Democrats redrew California's congressional maps last year, adding conservative parts of the North State once represented by the late Republican Rep. Doug LaMalfa and cutting out bluer regions in Sonoma and Lake counties.

That shift gave Jones an opening. After narrowly squeezing into second place in the primary, he erased a nearly 19-point gap by the general election. He built support on both the left and right, winning the endorsement of Our Revolution, the progressive group founded by Vermont Sen. Bernie Sanders, while also hiring Republican strategist Rob Stutzman and securing the backing of Ray Riehle, the Republican he narrowly defeated in the primary. His largest margins came in the new, conservative counties of Yuba, Sutter, Sacramento, Placer and Colusa.

Jones injected $14.8 million of his own money into the campaign, setting a record for the most self-funding by a congressional candidate in California history, according to David McCuan, a political science professor at Sonoma State University.

A former venture capitalist, Jones grew up in a working-class family in Maine that at times relied on Medicaid, food stamps and his father's veterans disability checks. He moved to Napa in 2021 with his wife after their son was born with a serious heart defect, seeking a slower life within driving distance of the boy's doctors at UCSF.

Thompson, who turned 75 this year, usually wins close to two-thirds of the vote in general elections. But this year he faced a wave of anti-establishment sentiment and desire for generational change that has swept challengers across the country. Nationally, 13 members of Congress lost their primaries, including seven Democrats and six Republicans.

The contest was also defined by blistering attack ads. Less than two weeks before Election Day, Jones' campaign released an ad featuring Thompson's former communications director, T.J. Adams-Falconer, who claimed, "Mike Thompson told me directly he plans to die in office." Thompson called the claim "fictional," and seven former staff members released a letter calling it "unsubstantiated" and demanding the ad be taken down because it used a photograph of them without permission.

At a campaign event in Napa County before polls closed, Thompson expressed confidence in his outreach to new voters, saying he had "approached this redistricting the same way I've approached every redistricting I've been in."

"There are 47% of voters who are new," he said. "I've got out, I've met folks, I think I've been a hundred times up in the new district, I've had a couple hundred meetings. And I've been called on to help with the peach farmer disaster. I was able to get them $9 million of aid."

Jones struck a conciliatory tone after the race was called, saying he is "very excited to work with Thompson in any way I can to do what's right for the district."

But McCuan said Jones could face a chilly reception from fellow Democrats in the House. "They're going to want to penalize him a little bit for taking on a popular incumbent and winning," he said.

Still, McCuan described the victory as "dramatic in terms of a statement about generational change," given Thompson's national stature and role in Democratic leadership.

For voters like Wendell Coleman, 50, an independent from Napa who said he used to vote for Thompson "religiously" until this year, Jones represents something new.

"He's relatable; he came from nothing, went to college. He's a role model for my daughter," Coleman said. "We need a fresh, new voice. We need someone that is self-made that can't be bought because he already has enough."