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.