The 10 Senate seats most likely to flip in 2018

Republicans are increasingly focused on the Senate as GOP donors and strategists grow more pessimistic about their ability to hold onto the House.

The prospect of a Democratic House has made Republicans desperate to take advantage of a favorable Senate map to hold or expand their majority in the upper chamber.

Republicans still have a strong chance of gaining seats, with 10 Democrats up in states President TrumpDonald John TrumpCNN analyst Kirsten Powers: Melania's jacket should read 'Let them eat cake' CNN's Cuomo confronts Lewandowski over 'womp womp' remark Sessions says FBI agent Peter Strzok no longer has his security clearance MORE won in 2016. But while the GOP is mostly on the offensive, the party also faces the prospect of losing some seats.

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Here’s a look at the top 10 seats most likely to flip in 2018:


1. Sen. Dean HellerDean Arthur HellerThe Hill's Morning Report — Sponsored by PhRMA — GOP lawmakers race to find an immigration fix 13 GOP senators ask administration to pause separation of immigrant families The Hill's Morning Report — Sponsored by PhRMA — Defiant Trump meets with House GOP amid border blowback MORE (R-Nev.)

Heller is the only Republican incumbent defending a seat in a state Democratic presidential nominee Hillary ClintonHillary Diane Rodham ClintonSessions says FBI agent Peter Strzok no longer has his security clearance Melania Trump puzzles with 'I really don't care' jacket Grassley wants to subpoena Comey, Lynch after critical IG report MORE won in 2016 — bad news for him as Democratic enthusiasm surges. His opponent, Rep. Jacky RosenJacklyn (Jacky) Sheryl RosenTrump to attend fundraiser for Heller Dems seek to seize on data privacy as midterm issue Danny Tarkanian wins Nevada GOP congressional primary MORE (D), has posted strong fundraising numbers and is trying to press Heller for his waffling on the GOP health-care repeal and his public role in crafting the GOP tax bill.

But Heller has recently seen a spate of good news that’s improved his chances of surviving in November. Primary challenger Danny Tarkanian dropped out of the race, allowing the senator to avoid making overtures to the GOP’s right flank that could hurt him in the general election. Republicans are also slowly cutting into Democrats’ voter registration advantage in Nevada.

2. Sen. Claire McCaskillClaire Conner McCaskillConservative group calls for ethics probe into McCaskill’s use of private plane Senate moderates hunt for compromise on family separation bill Election Countdown: Family separation policy may haunt GOP in November | Why Republican candidates are bracing for surprises | House Dems rake in record May haul | 'Dumpster fire' ad goes viral MORE (D-Mo.)

McCaskill has always faced a tough road to reelection. She’s one of just three Democrats elected statewide in Missouri, which Trump won by almost 20 points. And the GOP is already seizing on McCaskill’s ardent support for Clinton in 2016 as a way to rile up the base.

Still, she’s won a reputation as a strong campaigner and a consistently prolific fundraiser this cycle.

State Attorney General Josh Hawley is still considered a top GOP recruit. But Republicans are closely watching his first-quarter fundraising haul following grumblings about his disappointing fundraising pace last year. The investigations into blackmail allegations against Missouri Gov. Eric Greitens (R) could add a tinge of scandal to the Republican brand in the state.

3. Sen. Joe DonnellyJoseph (Joe) Simon DonnellyElection Countdown: Family separation policy may haunt GOP in November | Why Republican candidates are bracing for surprises | House Dems rake in record May haul | 'Dumpster fire' ad goes viral Actress Marcia Gay Harden urges Congress to boost Alzheimer's funding Manchin becomes final Democrat to back bill preventing separation of immigrant families MORE (D-Ind.)

The GOP primary between Rep. Luke MesserAllen (Luke) Lucas MesserGOP governors sign letter supporting Nobel Peace Prize for Trump These three Democrats are no sure thing in November The Hill's Morning Report — Sponsored by FICO — Paul Ryan’s rough ride MORE, Rep. Todd RokitaTheodore (Todd) Edward RokitaThese three Democrats are no sure thing in November The Hill's Morning Report — Sponsored by FICO — Paul Ryan’s rough ride Five takeaways from Tuesday’s primary fights MORE and businessman Mike Braun remains one of the nastiest in the nation. The bruising primary fight will also draw down GOP cash reserves before the general election.

The ferocity of the primary gives Donnelly space to position himself as a bipartisan legislator, and he posted his best fundraising total of his career last quarter. But Donnelly will still have a rough go in Vice President Pence’s backyard. The Democrat’s fundraising still falls far short of the totals raised by many other Democratic incumbents, and his Republican challenger will have months to build his funds back up.

4. Arizona’s open seat (vacated by GOP Sen. Jeff FlakeJeffrey (Jeff) Lane FlakeMcSally takes hard line on immigration in Arizona primary Flake threatens to limit Trump court nominees: report Poll: McSally holds 14-point lead in Arizona GOP Senate primary MORE)

Both parties think their leading candidates can win in Arizona. Reps. Martha McSallyMartha Elizabeth McSallyThe Hill's Morning Report — Sponsored by PhRMA — Trump caves under immense pressure — what now? McSally takes hard line on immigration in Arizona primary Election Countdown: Family separation policy may haunt GOP in November | Why Republican candidates are bracing for surprises | House Dems rake in record May haul | 'Dumpster fire' ad goes viral MORE (R) and Kyrsten Sinema (D) are strong fundraisers who know how to win tough fights. McSally is a veteran who can straddle the line between appealing to the right and to moderate voters, while Sinema is a Blue Dog Democrat with a compelling story who Democrats believe can compete statewide.

Sinema is a virtual lock for the Democratic nomination, but McSally has a rockier path in the GOP primary. She faces former state Sen. Kelli Ward and former Maricopa County Sheriff Joe Arpaio — two controversial candidates who could steer the race to the right. Arizona’s August primary is held late in the cycle, giving the GOP nominee just 10 weeks to recover from a potentially rough primary.

5. Sen. Heidi HeitkampMary (Heidi) Kathryn HeitkampSupreme Court rules states can require online sellers to collect sales tax Election Countdown: Family separation policy may haunt GOP in November | Why Republican candidates are bracing for surprises | House Dems rake in record May haul | 'Dumpster fire' ad goes viral Poll: GOP challenger narrowly leads Heitkamp in North Dakota MORE (D-N.D.)

Republicans caught a break when they convinced Rep. Kevin CramerKevin John CramerGOP lawmaker compares cages for migrant children to chain-link fences on playgrounds Election Countdown: Family separation policy may haunt GOP in November | Why Republican candidates are bracing for surprises | House Dems rake in record May haul | 'Dumpster fire' ad goes viral Overnight Health Care — Presented by the Association of American Medical Colleges — Trump officials move to expand non-ObamaCare health plans | 'Zero tolerance' policy stirs fears in health community | New ObamaCare repeal plan MORE to mount a late bid against Heitkamp. Cramer has made his campaign about fierce loyalty to Trump, who won the state by 36 points in 2016. Cramer can also run on the statewide name recognition he’s built up as a three-term congressman in an at-large seat.

But Republicans had wavered on Cramer before, looking for other alternatives to the gaffe-prone congressman before ultimately settling on him as the top choice. And while Trump repeatedly pushed Cramer to run, the president has also been on good terms with Heitkamp, who has appeared on stage with him in North Dakota and flew on Air Force One.

The escalating trade war between Trump and China could also dampen the GOP’s prospects. China’s retaliatory tariffs threaten to hurt jobs in the agriculture-heavy state, an issue that could weigh on Cramer.

6. Sen. Bill NelsonClarence (Bill) William NelsonFlorida lawmakers blocked from entering facility holding migrant children Transportation Department watchdog to examine airplane cabin evacuation standards Hillicon Valley: Supreme Court takes up Apple case | Senate votes to block ZTE deal | Officials testify on Clinton probe report | Russia's threat to undersea cables | Trump tells Pentagon to create 'space force' | FCC begins T-Mobile, Sprint deal review MORE (D-Fla.)

Gov. Rick Scott’s (R) Monday entry into the race is a big win for Republicans, who previously faced long odds taking the swing-state seat. Scott will give Nelson the toughest race of his Senate career. The two-term governor has a formidable campaign operation, and his vast personal wealth will be an asset in Florida’s pricey media markets.

But this will also be a much different race for Scott. In the past, he’s only run in Republican wave years, winning by razor-thin margins even when the political atmosphere favored the GOP. And his closeness to Trump, who personally recruited him for the Senate race, could also be a potential drag in a state the president won by a little more than a point.

7. Sen. Joe ManchinJoseph (Joe) ManchinThe Hill's Morning Report — Sponsored by PhRMA — Trump caves under immense pressure — what now? Election Countdown: Family separation policy may haunt GOP in November | Why Republican candidates are bracing for surprises | House Dems rake in record May haul | 'Dumpster fire' ad goes viral Manchin up 9 points over GOP challenger in W.Va. Senate race MORE (D-W.Va.)

Manchin faces an uphill climb keeping his seat in a state that went for Trump by nearly 42 points. But Manchin could benefit from a brutal GOP primary fight.

The two-person race between Rep. Evan JenkinsEvan Hollin JenkinsKey Republican says House taking targeted approach to combating opioid epidemic Dem candidate denies W.Va. is racist for rejecting Obama Dem House candidate in West Virginia voted for Trump MORE and state Attorney General Patrick Morrisey has been upended by a surge from former coal CEO Don Blankenship. Blankenship is polling well in the primary, even after serving a prison term over a fatal mine explosion. While Blankenship has the wealth to dominate the airwaves in the primary fight, Republicans fear he can’t win over more moderate voters in November.

Trump is going on the offensive against Manchin, after an initial show of bipartisanship with the senator. Flanked by Jenkins and Morrisey at a recent roundtable in West Virginia, Trump slammed Manchin for his vote against the tax overhaul.

8. Sen. Tammy BaldwinTammy Suzanne BaldwinMembers of Congress demand new federal gender pay audit Ellison introduces bill to curb stock buybacks Dem Senate super PAC reserves million in fall TV ads MORE (D-Wis.)

Wisconsin was once seen as a reach for Republicans. But the barrage of attack ads from outside GOP groups have softened Baldwin up ahead of November, prompting a flurry of Democratic spending meant to shore up the senator.

It’s still unclear who will emerge from the contentious GOP primary. Marine Corps veteran Kevin Nicholson, a former Democrat, is the pick of top conservative groups, but state Sen. Leah Vukmir has some big Wisconsin names in her corner.

9. Sen. Jon TesterJonathan (Jon) TesterOvernight Defense: Trump orders Pentagon to help house immigrant families | Mattis says 'space force' needs legislation | VA pick gets hearing date Election Countdown: Family separation policy may haunt GOP in November | Why Republican candidates are bracing for surprises | House Dems rake in record May haul | 'Dumpster fire' ad goes viral Senate panel schedules hearing on Trump VA pick MORE (D-Mont.)

Tester has built his campaign message around his willingness to work with Trump, a key argument in a state the president won by 20 points. And while the GOP hopefuls — state auditor Matt Rosendale, Judge Russ Fagg and businessman Troy Downing — are more focused on attacking Tester than blasting each other, the fluid primary still gives Tester some room.

Fortunately for Tester, Democrats aren’t extinct in Montana — Gov. Steve Bullock (D) cruised to reelection in 2016, even as Trump dominated.

Still, Tester has never won reelection with the majority of the vote, winning instead after a Libertarian candidate siphoned off votes from the GOP. This year, the presence of both a Green Party candidate and a Libertarian candidate on the ballot complicates that calculus.

10. Sen. Sherrod BrownSherrod Campbell BrownDem senators introduce bill to ban controversial voter purges The Hill's Morning Report — Sponsored by PhRMA — GOP lawmakers race to find an immigration fix Warren to put hold on Trump consumer bureau nominee MORE (D-Ohio)

Judging only by its 2016 numbers, Ohio should be more competitive. The state is drifting right — Trump won by 8 points, and all of the top statewide officeholders are Republicans. Still, the GOP has struggled to dent Brown, and he’s pulled in impressive fundraising totals.

Republican front-runner Rep. Jim RenacciJames (Jim) B. RenacciPence knocks Sherrod Brown in Ohio, boosts Renacci Poll: Casey holds double-digit lead over Barletta in Pa. Senate race Sherrod Brown tops GOP challenger by 17 points in Ohio Senate poll MORE has faced a spate of bad headlines in recent weeks about accusations that he failed to disclose political donations while registered as a lobbyist. He is looking to best businessman Mike Gibbons in the primary.

Other races to watch: Sen. Bob CaseyRobert (Bob) Patrick CaseyAction by Congress is needed to help victims of domestic violence Poll: Casey holds double-digit lead over Barletta in Pa. Senate race Ivanka Trump to press Senate on vocational training bill MORE Jr. (D) still appears in the driver’s seat in Pennsylvania, even as GOP Rep. Lou BarlettaLouis (Lou) James BarlettaPoll: Casey holds double-digit lead over Barletta in Pa. Senate race How lawmakers have landed an endorsement from Trump Pennsylvania lawmakers invite Eagles to Capitol after Trump snub MORE steps up his fundraising. Former Tennessee Gov. Phil Bredesen (D) raised eyebrows by polling ahead of GOP Rep. Marsha BlackburnMarsha BlackburnWhat the net neutrality repeal means Dem Senate super PAC reserves million in fall TV ads Scalise throws support behind Black, Blackburn ahead of Tennessee primary MORE for the seat currently held by retiring Sen. Bob CorkerRobert (Bob) Phillips CorkerOn The Money — Sponsored by Prudential — Senators hammers Ross on Trump tariffs | EU levies tariffs on US goods | Senate rejects Trump plan to claw back spending Senators hammer Ross over Trump tariffs GOP senator demands details on 'damaging' tariffs MORE (R), but she has time to boost her statewide name recognition. Mississippi’s special election is home to a four-way jungle primary that’s tough to handicap. And while Rep. Beto O’Rourke (R-Texas) is setting fundraising records, it’s unclear whether it’s enough to defeat Sen. Ted CruzRafael (Ted) Edward CruzSenate Gang of Four to meet next week on immigration Live coverage: High drama as hardline immigration bill fails, compromise vote delayed Trump renews call to end filibuster amid immigration furor MORE (R-Texas).