Senate Democrats are defending 10 seats President Donald Trump won last cycle. But a year out from Election Day, the most vulnerable senator is the lone Republican facing re-election in a state won by Hillary Clinton.The overall Senate landscape has improved for Democrats since the beginning of the year, with Republican retirements opening up two seats in 2018. But this ranking only features incumbents.

More GOP primaries could develop, but besides Nevada’s Dean Heller, the other nine most vulnerable senators are all Democrats.

Many of them have strong personal brands in their states, or even have a working relationship with the president. Meanwhile, Republicans have struggled to land top recruits or are locked in ugly primaries. But given the political bent of these states — which Trump won by anywhere from 42 points to 1 point — Democrats still have a challenging road ahead.

Heller is the only Republican up for re-election in a state Clinton won last fall. Nevada was one of the few Democratic bright spots in 2016, giving the party hope that the Silver State is turning blue. It’s Heller’s first time running for re-election to the Senate, and he is facing pressure from both the right and the left. Perennial candidate Danny Tarkanian has launched a GOP primary challenge, while Democratic Rep. Jacky Rosen is hoping to take on Heller in November. Heller struggled with balancing pressure from conservative and liberal forces when addressing health care, opposing some GOP plans but supporting others.

Republicans view Missouri as one of their top pickup opportunities. GOP presidential candidates have won the state each election since 2000, with Trump winning by 19 points in 2016. Missouri Attorney General Josh Hawley, first elected last year, is running on the GOP side. Republicans view the 37-year-old as a rising star. But Hawley will have to fend off charges of hypocrisy, since he ran an ad in his 2016 campaign criticizing politicians constantly running for higher office.

Donnelly defeated a flawed GOP candidate who made controversial comments about rape to win his first term in 2012. Now he’s running for re-election in a state that went for Trump by nearly 20 points. Three credible Republicans, two of whom serve with Donnelly in Washington, are tearing each other apart to take him on. The incumbent will have to stick to the nonpartisan image he tried cultivating in 2012 with his “Hoosier common sense” slogan. He’s voted for Supreme Court Justice Neil Gorsuch and has traveled on Air Force One with Trump. But Republicans are already going after him for owning stock, which he’s since sold, in a family company that manufactures some products in Mexico.A former governor, Manchin has a strong personal brand in West Virginia. But Trump won the state by more than 40 points, and Manchin was on record supporting Clinton last year. Two credible GOP challengers — Rep. Evan Jenkins and state Attorney General Patrick Morrisey — are going after each other, and both are eager to tie Manchin to Clinton’s 2016 comments about coal miners. As one of the most conservative Democrats in the Senate, Manchin has a relationship with Trump that may help him defend his Washington tenure in an increasingly red state.

Trump won the GOP-leaning state by 36 points, putting Heitkamp’s re-election in question. North Dakota has also shifted to the right. Republicans dominate all statewide offices, except for Heitkamp’s Senate seat. This is Heitkamp’s first time running for re-election to the Senate, and she won in 2012 by less than a point. But she has her own brand in the state, where she once served as attorney general. She has crafted a moderate profile in the Senate, supporting a number of the president’s nominees, including Gorsuch (Trump also referred to Heitkamp as a “good woman”). It’s not clear who Heitkamp will face in November, with the Republican field still in flux.

Tester has never crossed 50 percent of the vote in his previous Senate runs, and he’s now seeking a third term in a state Trump won by more than 20 points. Tester is a working farmer, but the former chairman of the Senate Democrats’ campaign arm doesn’t have as moderate a profile as some other red-state Democrats up for re-election this cycle. He voted against Gorsuch. The GOP field is crowded, but still unsettled after top recruits passed on the race. Steve Bannon and some national Republicans are lining up behind state Auditor Matt Rosendale.

Brown is facing a likely rematch against state Treasurer Josh Mandel, the Republican he defeated by 6 points in 2012. Even Republicans willingly admit Mandel has faults. But he also has proven fundraising ability — and name recognition from his previous campaigns. In a state that’s trending Republican — Trump carried it by 8 points last fall while GOP Sen. Rob Portman won re-election by over 20 points — Brown could be in for a tough race despite sticking to a strong anti-trade message.

Nelson’s running for a fourth term in a state Trump narrowly won. It’s all but assumed GOP Gov. Rick Scott will run against him, and if, as expected, he pours his own money into the race, this contest could get even more competitive. Nelson led Scott 37 percent to 36 percent in a mid-October survey of registered voters by the University of North Florida. But nearly half the respondents didn’t know how Nelson was handling his job as senator. Scott faced some negative headlines in the aftermath of Hurricane Irma, but still benefited from plenty of earned media during the storm.

Trump was the first GOP presidential nominee to win Wisconsin since 1984, but Republicans are typically successful in midterm elections in the Badger State. Baldwin was first elected in 2012, a good year for Democrats, after serving seven terms in the House. She could benefit from a primary on the Republican side, where GOP candidates will battle it out and expend resources ahead of the general election. She has also not shied away from liberal stances, and is, so far, the only Democrat running in a state Trump won who’s backed Sen. Bernie Sanders’ “Medicare for All” legislation.

Casey is running for a third term in a state Trump won by less than a point. Pennsylvania is a consistent swing state. A number of candidates are running on the Republican side, including GOP Rep. Lou Barletta, one of Trump’s earliest backers in Congress. Casey has been a vocal critic of the Trump administration. He railed against the GOP health care plan, which Barletta supported, and has also slammed Trump’s move to bar refugees from several Muslim-majority countries.

Graphics by Sara Wise/Roll Call

Data sources: Associated Press, Daily Kos Elections, states’ secretaries of state