Who Will Win Control of the House in 2024? California May Hold the Key.

As Democrats look to wrest control of the U.S. House of Representatives in November, their fight will fully begin with Tuesday’s primaries in California.

And their immediate trouble is not Republicans. It’s Democrats themselves.

In the Republican-held Central Valley district stretching from Bakersfield to Fresno, which would have favored President Biden by 13 percentage points in 2020, a battle between two Democrats has become so personal that some in the party fear they could divide the vote, leaving the incumbent, Representative David Valadao, competing in November against another Republican running to his right, Chris Mathys.

With so few truly contested seats to fight over this year, the prospect of an early lockout in California — where the top two finishers regardless of party affiliation compete in the general election — has brought out some heavy hitters, including Dolores Huerta, the 93-year-old labor and civil rights leader who co-founded the United Farm Workers with Cesar Chavez in 1962. She is suiting up again on behalf of former California Assemblyman Rudy Salas, the top choice of institutional Democrats. So is California’s governor, Gavin Newsom, who will rally voters for Mr. Salas on Sunday in an effort to box out the other Democratic candidate, State Senator Melissa Hurtado.

“I’m scared,” Ms. Huerta said on Thursday from the unassuming offices of her foundation, which is based in Bakersfield. “We need to do a lot more work.”

Control of Congress could be at stake. Of the 16 House districts won by Mr. Biden but currently in Republican hands, five are in California, making the state a linchpin of the party’s hopes of retaking the chamber, where Republicans currently hold a three-seat majority.

“It’s going to come down to these tossups, and Democrats would have to win around two-thirds of them to take the majority,” said Erin Covey, the House analyst at the nonpartisan Cook Political Report.

Only two of those 16 districts that Democrats are targeting — in the Tidewater region of Virginia and in Omaha — are in states with Republican governors.

The National Republican Congressional Committee, the campaign arm of House Republicans, calculated that two-thirds of the battle for control of the House will occur in states largely untouched by the presidential election. With no boost from the presidential organizing and get-out-the-vote efforts, N.R.C.C. officials have set up 24 field offices — the most ever — figuring they are on their own in defending the G.O.P.’s razor-thin majority.

Republicans have made it clear that they are eager to prosecute their case in blue territory. Conservatives have made gains in such states — especially in Southern California and in Long Island and other areas on the outskirts of New York City — by running on crime, the high cost of living and the influx of migrants. One major motivating issue for Democrats, abortion, has not had as much of an impact in states where voters see abortion rights as protected.

But Democrats will be playing on their home turf, with strong state-level organizations and weak Republican Party structures. And they insist that they are playing with a strong hand: the threat posed to abortion rights and other freedoms, including in Democratic states, by an all-Republican government with Mr. Trump at its helm. The possibility of a Trump White House and a Republican Senate could make the House a lone bulwark against complete G.O.P. control in Washington.

Democratic candidates say they understand they need to fight Republicans on issues like immigration. Will Rollins, a 39-year-old former federal prosecutor and Justice Department official running to flip the seat held by Representative Ken Calvert, Republican of California, said the G.O.P. had handed his party a “gift” when Republicans, at Mr. Trump’s behest, rejected a painstakingly negotiated bipartisan border security deal crafted in part by members of their own party.

“It is incumbent upon us to make these arguments and to run on issues that Republicans think they have the high ground: border, inflation and crime,” said Mr. Rollins, who ran in the same district, around Palm Springs, two years ago. He lost to Mr. Calvert, 70, by four points.

Mr. Calvert expressed confidence that nothing would change this time around. “Voters weren’t buying what Rollins was selling last time,” he said, “and they’re certainly not any more interested this time around in his radical, soft-on-crime policies.”

On the whole, Democrats start at a slight numerical disadvantage when it comes to taking back the House. Gerrymandering and the natural sorting of voters between dense urban areas that are heavily Democratic and vast rural districts that are strongly Republican have left vanishingly few in play.

The Center for Politics at the University of Virginia has rated just 10 Republican seats as tossups, nine of them in states with Democratic governors. Democrats hold only nine seats considered tossups, and only one in a state with a Republican governor.

Democrats would need five seats to win control of the House, and their prime California targets are the districts held by Mr. Valadao and Representatives John Duarte, Mike Garcia and Michelle Steel.

With so few opportunities, an unforced error taking Democrats out of play in Mr. Valadao’s district would loom large. In an interview, Mr. Salas did not discount the possibility, if Republicans come out in force to vote in a Super Tuesday presidential primary where Democrats appear to have less at stake.

“This could be a real scenario,” he said in an interview on Friday.

Ms. Hurtado was unapologetic in an interview last week over chile relleno at La Imperial Taqueria in Wasco, Calif., a town of 28,000 — if you count the prison population — surrounded at the moment by miles of blossoming almond trees.

“Obviously, I wasn’t the chosen one,” she said with a shrug. “But I like being the underdog.”

Democrats have improved their position in at least one California House race. Mr. Garcia’s district in northern Los Angeles County, redrawn in 2022, would have gone for Mr. Biden over Mr. Trump by more than 12 percentage points. Yet voters in the district nominated the same Democratic candidate, Christy Smith, three times against Mr. Garcia, and in every contest, Mr. Garcia beat her.

This time, Democrats have cleared the field for a new challenger, George Whitesides, a former NASA chief of staff and the former chief executive of the private space company Virgin Galactic. Mr. Whitesides has raised nearly $3.7 million, $271,000 of it his own money. Mr. Garcia has raised $3.2 million.

In an interview, Mr. Whitesides hit Mr. Garcia for selling as much as $50,000 in Boeing stock weeks before the House Committee on Transportation and Infrastructure released its highly critical investigation into the company’s 737 Max airliner, and talked up his own record in aerospace, in a district that relied on the industry.

“The fact that I’ve sort of created 700 jobs in the district helps a lot, too,” he said.

But infighting continues elsewhere. In a fierce fight for the Orange County seat vacated by Representative Katie Porter, a Democrat, State Senator Dave Min has been battling the political activist Joanna Weiss. Ms. Weiss has the backing of the pro-Israel United Democracy Project and Emily’s List, which works to elect female abortion-rights candidates. Those outside groups have pumped in more than $4 million against Mr. Min, Ms Covey said, and publicized charges of drunken driving and racism against him that will not make it any easier for Democrats to hold the seat.

That only makes the contest in Central Valley stand out more. When Democrats convinced Mr. Salas to run in 2022, he was considered a prized recruit, a popular state lawmaker who could have been the first Latino to represent the heavily Hispanic Central Valley.

That year, the drama was on the Republican side. Democrats tried to meddle in the so-called jungle primary by boosting Mr. Mathys, an ardent Trump supporter, in advertisements, hoping a hard-right candidate would be easier to beat than Mr. Valadao, who was one of just 10 Republicans to vote to impeach Mr. Trump for inciting the Jan. 6, 2021, attack on the Capitol. It didn’t work. Mr. Valadao beat Mr. Mathys by 1,220 votes for a distant second place behind Mr. Salas, and then stormed back to best the Democrat on Election Day by three points.

Democrats were ready to give Mr. Salas another chance this presidential election year, but Emily’s List convinced Ms. Hurtado to run as well, showing her data that indicated her vote totals in her State Senate races outpaced Mr. Salas’s votes in his House campaign.

Then Washington picked sides, fearing that Ms. Hurtado’s rise could leave Mr. Valadao and Mr. Mathys as the top two finishers on Tuesday.

House Majority PAC, the House Democratic leadership’s super PAC, is airing Spanish-language ads promoting Mr. Salas’s record on health care, while Mr. Salas, with the encouragement of Washington Democrats, has gone on air with an advertisement portraying Ms. Hurtado as hostile to abortion rights, for abstaining or missing votes on the issue in the State Senate. That was a painful expenditure for a candidate who has raised less than $747,000.

Ms. Hurtado, who has weathered more than $1 million worth of ads against her candidacy, has raised about a tenth of Mr. Salas’s total, $76,741. And Emily’s List does not include her as an endorsed candidate. But with the name recognition of a state senator whose district matches the U.S. House district by 95 percent, Democrats are sweating it out.

Ms. Hurtado is not, hoping that Mr. Salas’s negative ads will actually help her, especially with independents and Republican voters who have backed her in the past.

“If they were going to pick a side, they should have been upfront about it,” she said. “They could have said, ‘Step aside.’ They never did.”