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 Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate 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 Heller Dean Arthur HellerOn The Trail: Democrats plan to hammer Trump on Social Security, Medicare Lobbying World Democrats spend big to put Senate in play MORE (R-Nev.)

Heller is the only Republican incumbent defending a seat in a state Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE won in 2016 — bad news for him as Democratic enthusiasm surges. His opponent, Rep. Jacky Rosen Jacklyn (Jacky) Sheryl RosenHillicon Valley: Election officials prepare for new Russian interference battle | 'Markeyverse' of online fans helps take down a Kennedy | GOP senators unveil bill to update tech liability protections Google, Apple, eBay to meet virtually with lawmakers for tech group's annual fly-in Senate Democrats demand answers on migrant child trafficking during pandemic 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 McCaskill Claire Conner McCaskillMomentum growing among Republicans for Supreme Court vote before Election Day Democratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally 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 Donnelly Joseph (Joe) Simon DonnellyTrump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court Momentum growing among Republicans for Supreme Court vote before Election Day MORE (D-Ind.)

The GOP primary between Rep. Luke Messer Allen (Luke) Lucas MesserK Street giants scoop up coveted ex-lawmakers Yoder, Messer land on K Street House GOP to force members to give up leadership positions if running for higher office MORE, Rep. Todd Rokita Theodore (Todd) Edward RokitaIndiana attorney general loses reelection bid after groping allegations Bottom Line Lobbying world 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 Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE)

Both parties think their leading candidates can win in Arizona. Reps. Martha McSally Martha Elizabeth McSallyTumultuous court battle upends fight for Senate Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee The Hill's Campaign Report: Biden goes on offense 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 Heitkamp Mary (Heidi) Kathryn HeitkampCentrists, progressives rally around Harris pick for VP 70 former senators propose bipartisan caucus for incumbents Susan Collins set to play pivotal role in impeachment drama MORE (D-N.D.)

Republicans caught a break when they convinced Rep. Kevin Cramer Kevin John CramerMomentum growing among Republicans for Supreme Court vote before Election Day On Paycheck Protection Program, streamlined forgiveness is key McConnell shores up GOP support for coronavirus package 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 Nelson Clarence (Bill) William NelsonDemocrats sound alarm on possible election chaos Trump, facing trouble in Florida, goes all in NASA names DC headquarters after agency's first Black female engineer Mary W. Jackson 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 Manchin Joseph (Joe) ManchinThe Hill's Morning Report - Sponsored by Facebook - Trump, GOP allies prepare for SCOTUS nomination this week Trump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court 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 Jenkins Evan Hollin JenkinsWest Virginia New Members 2019 Republican Carol Miller holds off Democrat in West Virginia House race Trump to fundraise for 3 Republicans running for open seats: report 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 Baldwin Tammy Suzanne BaldwinKeep teachers in the classroom Cher raised million for Biden campaign at LGBTQ-themed fundraiser Democrats seek balance in backing protests, condemning violence 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 Tester Jonathan (Jon) TesterPence seeks to boost Daines in critical Montana Senate race This World Suicide Prevention Day, let's recommit to protecting the lives of our veterans Filibuster fight looms if Democrats retake Senate 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 Brown Sherrod Campbell BrownSenate Democrats release report alleging Trump admin undermined fair housing policies Bipartisan praise pours in after Ginsburg's death Emboldened Democrats haggle over 2021 agenda 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 Renacci James (Jim) B. RenacciOhio is suddenly a 2020 battleground Democrats fear Ohio slipping further away in 2020 Medicare for All won't deliver what Democrats promise 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 Casey Robert (Bob) Patrick CaseySecond GOP senator to quarantine after exposure to coronavirus GAO report finds brokers offered false info on coverage for pre-existing conditions Catholic group launches .7M campaign against Biden targeting swing-state voters MORE Jr. (D) still appears in the driver’s seat in Pennsylvania, even as GOP Rep. Lou Barletta Louis (Lou) James BarlettaBottom Line Ex-GOP congressman to lead group to protect Italian products from tariffs Head of Pennsylvania GOP resigns over alleged explicit texts MORE steps up his fundraising. Former Tennessee Gov. Phil Bredesen (D) raised eyebrows by polling ahead of GOP Rep. Marsha Blackburn Marsha BlackburnTaylor Swift on National Voter Registration Day: 'We need everyone' Democrats smell blood with new DHS whistleblower complaint Hillicon Valley: Election officials prepare for new Russian interference battle | 'Markeyverse' of online fans helps take down a Kennedy | GOP senators unveil bill to update tech liability protections MORE for the seat currently held by retiring Sen. Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump 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 Cruz Rafael (Ted) Edward CruzTrump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy MORE (R-Texas).