TURLOCK, Calif. — By most accounts, Rep. Jeff Denham is a strong incumbent. He has represented California’s Central Valley for four terms in Congress. His campaign signs line dusty street corners and the almond fields here in the state’s socially conservative agricultural region. He has raised nearly 3.5 million dollars this campaign season , about double the average raised by House members this year. In the primaries, 52 percent of his district’s vote went to Republican candidates.

If only his campaign could escape national politics.

For a variety of reasons, local elections are increasingly a referendum on what’s happening in Washington. As the number of media outlets shrinks, more news coverage is national. Partisanship is increasingly what drives people to the polls, and people vote in House races according to how they feel about whoever is in the White House. Incumbents have less of an advantage than they did in prior decades, and voters care less about experience than they used to.

All that — and a historically unpopular president — is making life harder for Republicans this midterm season. Denham held onto his seat in 2016, but his district went for Hillary Clinton (both he and Clinton won the region by 3 percentage points, and his district is less than 1 point more Republican-leaning than the nation as a whole ). He is not alone: 21 House Republicans are running for re-election in districts Clinton won in 2016, and 16 of those races are rated as toss-ups or are leaning toward Democrats, according to FiveThirtyEight’s model.

Can Republicans defend these vulnerable seats? FiveThirtyEight forecast ratings (as of Sept. 12) for Republican-held House districts that Clinton won in 2016 2016 vote margin District GOP Incumbent Clinton Incumbent SPREAD 538 rating TX-32 Pete Sessions* D+2 R+71 73 Likely R FL-27 Ileana Ros-Lehtinen** D+20 R+10 29 Solid D CA-21 David Valadao D+16 R+13 29 Lean R FL-26 Carlos Curbelo D+16 R+12 28 Toss-Up IL-06 Peter Roskam D+7 R+18 25 Lean R NY-24 John Katko D+4 R+21 25 Likely R WA-08 Dave Reichert** D+3 R+20 23 Toss-Up MN-03 Erik Paulsen D+9 R+14 23 Likely D CA-39 Ed Royce** D+9 R+14 23 Toss-Up CA-45 Mimi Walters D+5 R+17 23 Lean D AZ-02 Martha McSally** D+5 R+14 19 Likely D CA-48 Dana Rohrabacher D+2 R+17 18 Lean D CO-06 Mike Coffman D+9 R+8 17 Likely D VA-10 Barbara Comstock D+10 R+6 16 Likely D TX-07 John Culberson D+1 R+12 14 Toss-Up CA-25 Stephen Knight D+7 R+6 13 Likely D NJ-07 Leonard Lance D+1 R+11 12 Lean D KS-03 Kevin Yoder D+1 R+11 12 Lean R CA-49 Darrell Issa** D+8 R+1 8 Likely D CA-10 Jeff Denham D+3 R+3 6 Lean D TX-23 Will Hurd D+3 R+1 5 Toss-Up *No Democratic opponent in 2016

**Not running for re-election Source: DailyKos Elections, Individual state elections offices

For Denham and others, the question may be: Can they can keep voters’ frustrations with national politics out of their local elections?

The answer to that question could have particularly dramatic effects in California. Of the Golden State’s 53 congressional seats, just 14 are held by Republicans. But half of those Republican-led districts voted for Hillary Clinton in 2016. President Trump’s approval in the state has also gone from bad to worse since he was sworn into office. “The negative baggage that comes with being associated with [Trump’s] party, if it’s going to be felt anywhere, I think it’s going to be felt here,” said Gary Jacobson, an emeritus professor at the University of California, San Diego.

Republicans in the area have been trying to keep the election local in a variety of ways. For starters, they’ve cast Denham’s opponent, Democrat Josh Harder, as an outsider — not only to politics, but also to the area. They’ve criticized the time he spent at Stanford University and Harvard, as well as his early career working for a venture capital firm, where he ultimately rose to vice president. “[Denham’s] running against some Bay Area liberal, and I don’t think that guy can win,” said Jim DeMartini, the chairman of the Republican Party of Stanislaus County, which is in Denham’s 10th district, and a member of the county’s board of supervisors.

Harder says he’s no carpetbagger. He was born and raised in Turlock, a city of 74,000 in the 10th district, and he says his family still lives there. He frequently starts campaign speeches by explaining how his great-great-grandfather stopped 50 miles short of the gold he came looking for in the 1840s, becoming a peach farmer in Manteca instead. Since Harder moved home to run for office, he’s been teaching business at Modesto Junior College.

In campaign emails, Denham has also sought to bolster his war chest by highlighting the major source of Harder’s campaign funds: individuals living in Silicon Valley and San Francisco. (Harder’s campaign counters that the lion’s share of Denham’s campaign money, over 50 percent, comes from PACs, setting up a strange competition of which is more shadowy: liberal elites or big political money?)

And then there’s one of the most pressing local issues: water. The Central Valley, the state’s low-lying agricultural region, has an ongoing debate with more liberal, coastal parts of the state over how much water should go where. Water is essential to the area’s economy, but the precious commodity is constantly debated in this parched state. The Denham campaign also frequently invokes Harder’s absence from a recent rally at the state capitol as a sign that he doesn’t understand the needs of the area. “The day Josh Harder lost this election was the day state Democrats moved forward in a push to steal 40 percent of our water,” said Josh Whitfield, Denham’s campaign manager. Harder, meanwhile, contends that Denham’s vote to prohibit judicial review on a plan that would make it easier to deliver water from northern California to southern parts of the state helped other GOP-controlled districts at the expense of Denham’s own.

As much as Denham may want to make the race about local issues, national politics will still influence voters. That fact holds both promise and pitfalls for Denham and Harder. Republicans and centrist Democrats have long ruled the Central Valley, and Harder’s progressive agenda, which includes Medicare For All and comprehensive immigration reform, is a sharp departure from local politics of yore. Some lifelong Democrats think the shift is a positive one. “He’s encouraging young people and listening to their ideas. I think that’s good for the party!” said Pat Howell, the 74-year-old treasurer of a local Democratic Club, over the din of a crowded campaign event at an American Legion Hall. But others worry it’s a step too far; an audience member expressed skepticism at the potential cost of a Medicare For All system, asking Harder to explain what he saw in the plan.

But even if Harder’s positions may be too liberal for some, Denham’s voting record doesn’t show him to be ideologically distinct from a Republican Party that’s losing favor in the area. He’s voted in line with Trump 97.8 percent of the time according to FiveThirtyEight’s vote tracker, a much larger share than anticipated given how his district voted in 2016. In 2017, he voted to repeal and replace the Affordable Care Act in a district where an estimated 50,000 people would have lost coverage if the bill had passed. And though he has publicly taken a moderate stance on immigration, he led and then gave up on an effort to force a House vote on several immigration bills after promising he had the votes to get a package through.

Democrats, meanwhile, are relying on what’s happening in Washington to bring unexpected voters to the polls. Frustration with national politics could galvanize a historically disorganized base, said Juan Vazquez, a former farmworker from the Modesto area who now commutes to work at a Tesla plant in the East Bay. Vazquez says he considered himself a Republican and even liked Trump until the then-candidate referred to Mexicans as rapists at the beginning of his campaign. “He’s talking about me. I am from Mexico. My whole family is. We came to the United States to work in the fields, to work in agriculture,” he said. He’s since become politically active, and is a member of the Stanislaus County Democratic Central Committee.

But many Central Valley Latinos, a group that tends to lean Democrat, haven’t voted in the past. That may be connected to their history — some are immigrants who came from areas with corrupt governments where voting didn’t seem to matter — or they may not have voted because they felt like outsiders who shouldn’t participate, said Julissa Ruiz Ramirez, a college student at California State University, Stanislaus in Turlock who came to the U.S. when she was 4 and became a U.S. citizen last year. That was the sense she got from family and friends growing up, but she has decided to take a different route, majoring in political science and spending her free time campaigning for immigrants’ rights. She’s also a volunteer for the Harder campaign.

California’s 10th district is one of seven in the state that voted for Clinton in 2016 but is currently represented by a Republican in Congress. Each district has its own local issues that animate it, but they all have one thing in common: When you factor in fundraising, historical trends and the generic ballot, the Republican incumbents look like they are on much shakier ground than they would have been in previous elections. This midterm election, no House race is taking place in a vacuum.