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Six Months Out: The 10 Most Vulnerable Senators in 2018

Nevada Republican Dean Heller remains in top spot

Sen. Dean Heller is the only Republican running for re-election in a state Hillary Clinton won in 2016. (Bill Clark/CQ Roll Call file photo)
Sen. Dean Heller is the only Republican running for re-election in a state Hillary Clinton won in 2016. (Bill Clark/CQ Roll Call file photo)

Senate Democrats are still defending 10 states that President Donald Trump won in 2016, but six months out from Election Day, the most vulnerable senator remains a Republican.

Nevada Sen. Dean Heller no longer faces a primary threat, but he’s the only Republican up for re-election in a state Hillary Clinton won, and in this national environment that’s a tricky place to be.

The Democrats’ odds of flipping a few GOP-held open seats in Arizona and Tennessee have increased over the past six months, but this list — like the one we did a year out from Election Day — ranks incumbents most likely to lose — not seats most likely to flip. That means nine of the 10 senators are Democrats, with the second and third spots remaining unchanged.

North Dakota Sen. Heidi Heitkamp and West Virginia Sen. Joe Manchin III have traded places, with Heitkamp now at fourth and Manchin at fifth. Democrats would have been happy to face Don Blankenship in the West Virginia Senate race, but they’re also not getting Rep. Evan Jenkins, whom they spent nearly $2 million against in the primary.

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The biggest change is Florida Sen. Bill Nelson moving up from eighth to sixth with Gov. Rick Scott’s entry into the race. That pushes Montana Sen. Jon Tester and Ohio Sen. Sherrod Brown down a spot each to seventh and eighth, respectively.

As always, this list is compiled after consultation with strategists from both sides of the aisle and the race ratings from Inside Elections with Nathan L. Gonzales.


Heller remains at the top spot because he’s the only Republican up for re-election in a state Clinton carried in 2016, and Democrats have a favorable national environment this cycle. Heller has one less hurdle with perennial candidate Danny Tarkanian dropping his primary challenge to run for the House, at Trump’s urging. Democrats contend Heller moving toward Trump while Tarkanian was in the race could come back to haunt him. They have coalesced around Rep. Jacky Rosen, who is already up on television. (She does have a self-funding primary challenger.) Rosen raised more than twice as much as Heller in the first quarter of the year, pulling in $2.6 million to Heller’s $1.1 million. But Heller still has a cash on hand advantage.


Although some Republicans have fretted that likely GOP challenger Josh Hawley wasn’t living up to expectations, McCaskill is still one of the most vulnerable incumbents. Hawley’s fundraising caused some concern, but he also shook up his team, bringing in experienced GOP fundraiser Katie Walsh, according to Politico. Some operatives say Hawley could be hurt by his connection to disgraced Missouri GOP Gov. Eric Greitens, but Hawley’s team says the scandals won’t affect him. Republicans say Missouri is moving to the right, and point to Trump’s continued popularity in the Show-Me State.


Former state Rep. Mike Braun, who touts himself as a businessman outsider in the mold of Trump, is taking on the first-term Democratic senator. In a big Trump state, Donnelly’s got his work cut out for him, as Braun — who’s got plenty of his own money — will try to tie him to Washington, much like he did his two primary opponents. But Braun’s state legislative record and business background comes with its own vulnerabilities, and Donnelly has proved willing to support the president at times.


Heitkamp is the only statewide Democratic official in North Dakota, and Republicans believe the state’s shift to the right means she’s in serious trouble this year. Her challenger, GOP Rep. Kevin Cramer, has the advantage of not facing a primary. As the state’s at-large member, he also enjoys high name recognition. Heitkamp does still have a cash on hand advantage with $5.4 million in the bank, compared to Cramer’s $1.9 million. Democrats believe Heitkamp has a strong personal brand in the state as an independent lawmaker.


Facing state Attorney General Patrick Morrisey in November, Manchin’s in for a tough race in a state that went big for Trump. Morrisey will tout his lawsuits against the Obama administration and hammer Manchin on his support for Clinton in 2016. But Morrisey’s not without his own ties to Washington and the pharmaceutical industry, which could complicate the GOP playbook. The senator has a significant cash-on-hand advantage.


The three-term senator moves up the list because of the entrance of Gov. Rick Scott into this race. With statewide name identification and endless personal resources, Scott poses a real threat to Nelson, even in a state that’s more Democratic than the home states of some other senators appearing lower on the list. Nelson ended the first quarter with $10.7 million, while Scott hasn’t had to file a fundraising report yet.


Trump took aim at Tester, even calling on him to resign, over his resistance to the president’s VA nominee. Along with Tester’s vote against a stopgap funding measure that would have reopened the government earlier this year, Republicans think they have a strong case against the former DSCC chairman. Tester’s never taken more than 50 percent in his prior Senate races. But it’s also possible that as the senior Democrat on the Veterans Affairs Committee, Tester has helped solidify his own brand in Big Sky Country by doing what he thought was best for veterans. It’s looking like he’ll face fellow flat-top Matt Rosendale, who will likely be attacked as a carpetbagger from Maryland. Tester ended the first quarter with nearly $7 million to Rosendale’s $541,000.


Wisconsin has attracted the most outside spending of the Senate races so far, in part because Republicans view Baldwin as vulnerable on issues relating to veterans’ health care. But Democrats are watching for a potentially ugly primary between the two GOP candidates: state Sen. Leah Vukmir and Marine veteran Kevin Nicolson. Baldwin has kept her focus on the general election, airing five television ads so far. Republicans still believe she is very vulnerable and too liberal for the state (she was the only red state Democrat to sign on to Medicare-for-All legislation).


One major change since the last iteration of this list: Rep. James B. Renacci is now the Republican nominee here, not state Treasurer Josh Mandel, as was long expected. Brown’s running for re-election in a state that’s trending away from Democrats, but Renacci — a wealthy congressman and former registered lobbyist — should quiet attacks on Brown for being part of Washington. Although Renacci has plenty of his own resources, Republicans haven’t been impressed with his fundraising. His latest FEC filing shows $4.2 million in the bank to Brown’s $13.3 million.


Republicans and Democrats acknowledge that Casey is one of the least vulnerable Democratic senators running in states Trump carried in 2016. One of Trump’s early allies, GOP Rep. Lou Barletta, appears to be the likely nominee. Casey has broken fundraising records with more than $10 million on hand — the most of any Senate candidate in the state’s history according to Casey’s campaign. Barletta had $1.3 million on hand at the end of this year’s first quarter.

Graphics by Sara Wise

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