Republicans entered 2017 dreaming of dramatically expanding their Senate majority. But after a bruising year capped off by Democrat Doug Jones' upset victory in Alabama, the GOP is staring at a 2018 with diminished ambitions.

Still, the GOP will be on offense in 2018. Despite a favorable political environment driven by President Donald Trump's poor public standing, Democrats still only have two real pick-up opportunities next November, in Nevada and Arizona. Texas? Too expensive to attack with so much ground to defend. Tennessee? The party landed its dream recruit in former Gov. Phil Bredesen, but Trump won the state by 26 points in 2016.


While the field is tilted toward Democrats, the map still isn't. Democrats are still defending five states Trump won by double-digits, and another five he won more narrowly. In some of these states (Pennsylvania, Michigan), public polling has indicated Trump’s popularity is slipping and there’s a population of college-educated voters who dislike the president to lift Democratic incumbents. Polling in other states (Missouri and Indiana) indicate the president is holding strong and will likely be an asset for GOP candidates.

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Here’s POLITICO’s list of the top 10 Senate races of 2018, ranked by how likely they are to change parties:

1. Nevada — GOP Sen. Dean Heller running for reelection

Hillary Clinton only won Nevada by 4 points last year, while Trump won some of the Democratic-held states on this list by much larger margins. But a brutal political environment for Republicans — along with some potential missteps by Heller — make him the most vulnerable senator in 2018. Heller’s dramatic reversal of Obamacare repeal — staunchly opposing its initial versions, only to support Graham-Cassidy — was seemingly tailor-made for Democratic admakers, even if it helps him fend off Danny Tarkanian, his conservative primary challenger. Republicans will try to tie Rep. Jacky Rosen, his likely Democratic opponent, to Harry Reid and Nancy Pelosi. But it’s unclear that’s a winning strategy in a blue-tinted state in a Democratic year.

Sen. Claire McCaskill speaks to reporters Dec. 19. | John Shinkle/POLITICO

2. Missouri — Democratic Sen. Claire McCaskill running for reelection

McCaskill is facing 37-year-old Attorney General Josh Hawley — a top GOP recruit who already has multiple big money super PACs lined up to support him and the backing of Trump, Senate Majority Leader Mitch McConnell and former White House strategist Steve Bannon. Democrats had hoped a tricky primary could trip up Hawley, but most of the other top contenders dropped out. McCaskill, who has held 50 town halls this year, remains the craftiest politician running for Senate, however, and is expected to take a populist tack against the Stanford- and Yale-educated Hawley.

Sen. Joe Donnelly is a Democrat running for re-election in 2018 in a state that supported President Donald Trump. | J. Scott Applewhite/AP Photo

3. Indiana — Democratic Sen. Joe Donnelly running for reelection

Donnelly, like McCaskill, is running for reelection in a state Trump won handily. But while McCaskill is already locked in to a one-on-one matchup with Hawley, Donnelly will get to watch three different GOP primary contenders — Reps. Todd Rokita and Luke Messer, along with self-funding businessman Mike Braun — beat up on each other until the primary in May. Republicans believe they landed a major hit on Donnelly when the Associated Press reported he profited from a family company outsourcing jobs to Mexico. Donnelly sold his stock in the company after the story was published.

4. Arizona — Open; GOP Sen. Jeff Flake retiring

Flake’s retirement this summer came as it became increasingly clear he had no path to winning reelection. Establishment Republicans are now putting their faith in Rep. Martha McSally, one of the first female fighter pilots in the Air Force. McConnell touted McSally as a top recruit at his year-end press conference last week, even though she is yet to officially enter the race. Democratic Rep. Kyrsten Sinema, meanwhile, has cultivated a moderate profile in the House and might be the DSCC’s best recruit of the cycle. But it’s unclear how her progressive past will play in a state Trump won, even if it’s rapidly getting bluer.

5. North Dakota — Democratic Sen. Heidi Heitkamp running for reelection

North Dakota, along with West Virginia and Montana, is part of a trio of states where Trump won by double-digits, but Democrats have sitting senators with strong individual brands. Heitkamp’s work on farm and energy issues has separated herself from the national party, but GOP internal surveys released publicly consistently show her trailing Republicans by small margins. The big problem for Republicans: It’s not clear who their candidate is. Republicans have looked at both wealthy former state legislator Tom Campbell and Rep. Kevin Cramer and found them wanting. (Campbell is in; Cramer is still considering it.) Other Republicans, including state Treasurer Kelly Schmidt, have opted against a run.

6. West Virginia — Democratic Sen. Joe Manchin running for reelection

Manchin is a unique politician who has survived in West Virginia even as the state has turned bright red, giving Trump 69 percent of the vote in 2016. And more than other Democratic senators, Manchin has worked to ingratiate himself with Trump. He faces two potentially strong challengers in 2018 in Attorney General Patrick Morrisey and Rep. Evan Jenkins, although limited public polling has shown him starting with a lead over both men. Republicans are confident they can bring his numbers down by linking him to Mylan, a controversial pharmaceutical company where his daughter is CEO.

7. Ohio — Democratic Sen. Sherrod Brown running for reelection

A likely rematch of Brown's 2012 victory over state Treasurer Josh Mandel will be fought on altered terrain. That year, Brown appealed to the same blue-collar voters that embraced Trump in 2016. Mandel, meanwhile, has spent the past six years making as many enemies as allies in GOP politics: He endorsed Florida Sen. Marco Rubio over his home-state governor, John Kasich, and hasn’t endeared himself to Republicans in Washington. If he defeats businessman Mike Gibbons in the primary, Mandel, a strong fundraiser, will have the money to challenge Brown across Ohio’s expensive television markets.

8. Florida — Democratic Sen. Bill Nelson running for reelection

GOP Gov. Rick Scott is crucial to his party's 2018 Senate strategy. If the two-term governor enters the race, his showdown with Nelson will instantly become one of the nation's marquee Senate races. Republicans imagine Scott, who has immense personal wealth and is a strong fundraiser, outspending Nelson and forcing Democratic groups to spend in Florida’s multiple expensive markets, limiting their ability to defend other incumbents or go on offense. But if Scott doesn’t run, both parties expect Nelson will more or less cruise to reelection. When might Scott announce his decision? "[H]e'll make [an announcement] when he damn well wants," a political adviser told POLITICO earlier this year.

Sen. Jon Tester heads to a policy luncheon on Dec. 5. | John Shinkle/POLITICO

9. Montana — Democratic Sen. Jon Tester running for reelection

Of the triumvirate of Manchin, Heitkamp and Tester mentioned earlier, both parties think Tester is the safest for now. Trump's 56 percent vote share in Montana is smaller than in North Dakota or West Virginia. Tester, who returns from D.C. to work on his farm every weekend, has a strong brand. The front-runner to challenge him is state Auditor Matt Rosendale, but he’ll have to defeat businessman and veteran Troy Downing, and a number of other Republicans, in a primary.

10. Wisconsin — Democratic Sen. Tammy Baldwin running for reelection

Republicans in Wisconsin, who have taken over state government and helped guide Sen. Ron Johnson to an upset win in 2016, will insist Baldwin should be higher on this list. Baldwin is clearly left of the state’s political center. But she can also emphasize her points of agreement with Trump on trade, outsourcing and other issues. Wisconsin (along with Pennsylvania and Minnesota, two other Rust Belt states in which Trump made gains that have Democratic senators facing reelection in 2018), also has a significant population of suburban white college-educated voters who have turned against Republicans in special elections this year. State Sen. Leah Vukmir and businessman and veteran Kevin Nicholson are competing in the primary to take on Baldwin.

Honorable mentions (in alphabetical order): Michigan, Minnesota, New Jersey, Pennsylvania, Tennessee and Texas

Democrats expected Sen. Debbie Stabenow to stay safe in Michigan, although Republicans warn veteran John James could be a stronger-than-expected candidate if he wins the GOP primary. Lt. Gov. Tina Smith will take over one of Minnesota’s Senate seats from Al Franken at the start of January, and she could face a tough race if former Gov. Tim Pawlenty gets in. In a worse political environment, Sen. Bob Menendez’s recent trial on corruption changes might make his New Jersey seat vulnerable. Right now, he should be safe unless the Justice Department decides to retry him. Pennsylvania Sen. Bob Casey’s rhetoric has moved dramatically to the left heading into his reelection bid, but he’ll start with a big cash on hand advantage over Rep. Lou Barletta, a Trump ally. Bredesen is a top-flight recruit for Democrats in Tennessee, but whether the state will still embrace his moderate Democratic brand is up in the air. Rep. Beto O'Rourke is campaigning hard against Texas Sen. Ted Cruz, but the state is likely too expensive for Democrats to help him.