One year out from the 2020 elections, the most vulnerable member of the House is the Oklahoma Democrat whose upset win surprised even astute politicos last fall. She is joined by a California Republican who is under indictment and numerous Democrats running in districts President Donald Trump easily won in 2016.

Republicans need a net gain of 19 seats to win control of the House, and they see their path back to the majority running through so-called Trump districts that slipped from the party’s grasp in the midterms. Whether they succeed depends on next year’s political climate and the strength of their candidates. In some districts, the GOP has worked hard to recruit more diverse challengers, especially after Democrats’ success electing women last year.

Some members who did not make the list, such as Iowa Republican Steve King and Illinois Democrat Daniel Lipinski, could also be unseated in primaries next year. Michigan Rep. Justin Amash, who left the GOP to become an independent, is also in danger from his former party. But those races are still taking shape.

[See October 2020 updates to lists of most vulnerable House members and senators]

The only other Republican on the list is Pennsylvania’s Scott Perry, who’s facing a top Democratic recruit in a district that’s now less favorable to his party. Given that his district still voted for Trump, though, he comes in at the bottom of the list.

The only two Republicans running for reelection in districts Hillary Clinton carried — Pennsylvania’s Brian Fitzpatrick and New York’s John Katko — are not among the 10 most vulnerable because neither has a clear challenger yet, and both have survived in difficult environments before.

This list excludes open seats, even those where retirements may present good pickup chances for the opposite party. Democrats, for example, see opportunities in open seats in Texas.

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Rankings are based on past election results in each district, conversations with strategists on both sides of the aisle and race ratings from Inside Elections with Nathan L. Gonzales. But it’s still early, with plenty of time for new challengers to emerge, primary fields to shake out, and even some of these 10 members to decide not to run for reelection.

On this list, members’ names are followed by Trump’s winning (or losing) margin in the district, the member’s margin of victory in his or her most recent election, and the race rating from Inside Elections.

Horn’s district in Oklahoma City and its suburbs gave the president one of his biggest 2016 victories of the 31 Trump districts now held by Democrats. That 14-point margin alone has campaign operatives from both parties questioning Horn’s chances of winning another term.

She is the first Democrat in nearly 40 years to represent the Oklahoma City area in the House. Democrats argue that the region is changing, with downtown development drawing young, educated professionals and a rapidly expanding Hispanic population that is more inclined to vote for Democrats.

Her GOP challenger will have to win a primary first. Republicans are consolidating around state Sen. Stephanie Bice and businesswoman Terry Neese, either of whom they say would be a better fit for the district.

Horn is so far out-fundraising them both, with $1.2 million in cash on hand on Sept. 30, compared to $643,000 for Neese and $217,000 for Bice.

Hunter narrowly won reelection last year after being indicted for misusing campaign funds. In California’s primary system, all candidates, regardless of party, run on the same ballot with the top two vote-getters advancing to the general election.

Hunter not only faces his 2018 Democratic opponent, Ammar Campa-Najjar, he also has to contend with two well-known Republicans: former Rep. Darrell Issa, who represented a neighboring district, and talk radio host and activist Carl DeMaio, who ran unsuccessfully for a different House seat in 2014.

With a January trial ahead, it’s possible that Hunter may resign or decide to retire before the December filing deadline, but so far he has insisted he’s running.

This freshman narrowly won a longtime Republican seat in the Charleston area, in part by using his opposition to offshore drilling to draw a contrast with his GOP opponent, who had defeated Rep. Mark Sanford, a former governor and outspoken Trump critic, in the primary. Cunningham is likely to face a stronger opponent this time around, and with Trump on the ballot, it may be difficult for him to hold on. But he’s raising good money ($529,000 in the third quarter) and can tout a bill to ban offshore drilling that passed the House in September (though it’s headed nowhere in the Senate). He was one of a handful of vulnerable Democrats who held out support for an impeachment inquiry into Trump before backing a resolution on Oct. 31 that sets ground rules for the public portion of the probe.

It’s unclear how Rose’s public support for the impeachment inquiry, and his vote on the rules resolution, could affect his reelection, but Trump is popular in the 11th District, which includes Staten Island and a sliver of Brooklyn. GOP leadership has signaled that Assemblywoman Nicole Malliotakis is their preferred candidate. She carried the 11th District when she ran unsuccessfully for New York mayor in 2017. It’s still unclear, though, whether former GOP Rep. Michael G. Grimm, who served prison time for tax fraud, will jump in the race. Rose has continued to build his war chest, raising nearly $735,000 in the third quarter compared to Malliotakis’ $206,000.

McAdams is the only Democrat in Congress representing heavily Republican Utah. His name recognition and popularity at home — he is the former mayor of Salt Lake County — helped him unseat two-term GOP Rep. Mia Love in 2018. But a growing field of Republicans will be vying for the chance to challenge him, including state Sen. Dan Hemmert, who has ties to the popular Republican Sen. Mitt Romney.

Of the 43 seats Democrats flipped in 2018, Brindisi’s backed Trump by the highest margin two years earlier. Republicans believe Trump’s presence on the 2020 ballot will bring out his supporters in this upstate New York district who stayed home in 2018, dooming Brindisi. But Democrats believe the incumbent’s strength in fundraising, name recognition and his tendency to break with his party — he was long a holdout on backing the impeachment inquiry before voting in favor of the rules measure — could make him tough to beat. Brindisi could face a rematch with the Republican he unseated, Claudia Tenney, who has been known to make controversial comments.

Trump’s large margin of victory in 2016, and Torres Small’s narrow win two years later, puts this New Mexico seat in the GOP’s sights. But Democrats say Torres Small, a water rights lawyer whose campaign videos showed off her rifle skills, is a perfect fit for the rural district. There’s a good chance the 2020 election will be a rematch with her 2018 rival, former state Rep. Yvette Herrell, who has rebuilt her campaign team. Republicans are also excited about Claire Chase, the former chairwoman of the New Mexico Oil and Gas Association. It’s unclear, though, how Chase’s record as a onetime Trump critic will play in a GOP primary, especially after publicity over a 2015 Facebook post in which she used an expletive and said Trump was “unworthy of the office.”

The chairman of the Agriculture Committee is widely regarded as the last Democrat who can hold on to this sprawling, rural district. Peterson is one of the most conservative Democrats in the House — he’s voted with Trump more than any other Democrat, according to CQ Vote Watch, and he was one of just two Democrats to vote against the impeachment inquiry rules resolution — but that might not be enough to save him. He only narrowly defeated an underfunded GOP challenger the past two cycles, but in 2020, he’s likely to face a much stronger opponent in former Minnesota Lt. Gov. Michelle Fischbach, a recruit national Republicans are excited about.

Finkenauer is facing one of the Republicans’ top recruits, state Rep. Ashley Hinson, who represents a swing legislative district and worked as a television journalist in Cedar Rapids. Republicans believe the presidential race and a competitive Senate race could drive out Trump voters in Iowa and help defeat Democrats like Finkenauer and Rep. Cindy Axne, who flipped Iowa’s 3rd District in 2018. Some operatives see Finkenauer’s race as more fertile GOP ground because Axne’s district is more suburban and has a higher percentage of college-educated voters. But Finkenauer could still be tough to beat. She was a state legislator before her election to Congress, has connections to unions, and still has a sizable cash-on-hand advantage.

Perry is running for only the second time under his district’s current configuration. In 2018, the state Supreme Court tossed out Pennsylvania’s congressional map as a partisan gerrymander. Perry’s south-central district became more competitive, and about 40 percent of it was new to him, according to calculations by Daily Kos Elections. Trump would have still won the district under the new lines. Perry, a member of the hard-line conservative House Freedom Caucus, eked out a win last year, making him a Democratic target in 2020. He faces state auditor Eugene DePasquale, who narrowly carried the district in his auditor race in 2016 and got off to a fast fundraising start. DePasquale raised about $360,000 to Perry’s $299,000 in the three months ending Sept. 30, though the incumbent ended the quarter with more cash on hand.