GOP to retain Senate majority

Republicans are guaranteed to keep control of the Senate after netting early victories by flipping four Democratic seats and winning a marquee race in Texas.

GOP candidates scored major victories in Indiana, Missouri and North Dakota, while several other toss-up races remain too close to call, paving the way for the party to potentially expand its 51-49 majority.

Businessman Mike Braun (R) unseated Sen. Joe Donnelly (D-Ind.) — marking the first red-state Democrat to lose on Tuesday and giving the GOP an early seat flip.

Three more Democrats followed: Sens. Heidi HeitkampMary (Heidi) Kathryn HeitkampTrump nominees meet fiercest opposition from Warren, Sanders, Gillibrand McConnell's Democratic challenger McGrath backtracks on Kavanaugh comments McConnell's Democratic challenger says she likely would have voted for Kavanaugh MORE (N.D.), Claire McCaskillClaire Conner McCaskillTrump nominees meet fiercest opposition from Warren, Sanders, Gillibrand Feds allow campaigns to accept discounted cybersecurity services GOP frets over nightmare scenario for Senate primaries MORE (Mo.) and Bill NelsonClarence (Bill) William NelsonDemocrats target Florida Hispanics in 2020 Poll: Six Democrats lead Trump in Florida match-ups How Jim Bridenstine recruited an old enemy to advise NASA MORE (Fla.).

The red-state Democratic losses came after Republicans avoided a major upset in Texas, where Rep. Beto O'RourkeBeto O'RourkeThe Hill's 12:30 Report: Trump digs in ahead of House vote to condemn tweet Poll: Biden, Sanders and Warren lead 2020 Democrats in New Hampshire Poll: Biden leads 2020 Democrats by 13 points, followed by Sanders, Warren and Harris MORE (D) shot into an early lead but was ultimately unable to overcome Sen. Ted CruzRafael (Ted) Edward CruzGoogle official denies allegations of ties to China The Hill's Morning Report - Presented by JUUL Labs - House to vote to condemn Trump tweet Cruz in 2016 said 'something fundamentally wrong' with Christians who back Trump: book MORE (R).

Absent a last-minute upset in a seat controlled by Republicans, the three Democratic losses and the GOP win in Texas guarantees Republicans will hold onto the chamber, even with undecided races in Arizona and Nevada.

Democrats entered Election Day looking to defend seats in 10 states that Trump won in 2016, presenting them with an uphill battle to take back the Senate or maintain the GOP's slim majority.

Sen. Jon Tester (Mont.) is the last vulnerable Democrat whose race has yet to be called. Though he remains in the lead against GOP challenger Matt Rosendale, the race has tightened as more precincts have begun reporting.

One race that will not be decided on Tuesday is a special election in Mississippi, where Sen. Cindy Hyde-Smith (R) was hoping to prevent a runoff election for her Senate seat.

Hyde-Smith and Democrat Mike Espy, as the top two candidates, will advance to a Nov. 27 runoff, but the outcome of that race will not determine control of the Senate.

Even with the Mississippi race undecided, Democrats could sweep the remaining battleground states and fall short, with Republicans holding a 52-47 majority in that scenario.

If Democrats sweep the remaining battleground states and Republicans ultimately win Mississippi, where Trump remains popular, that would give Republicans a 53-47 majority.

Democrats have gotten some good news on Tuesday night. Sen. Joe ManchinJoseph (Joe) ManchinTrump nominees meet fiercest opposition from Warren, Sanders, Gillibrand Kentucky Democrat says primary challenge to McGrath 'might be helpful' McConnell's Democratic challenger McGrath backtracks on Kavanaugh comments MORE (D-W.Va.) held off state Attorney General Patrick Morrisey in what was expected to be a competitive race.

Meanwhile, Sen. Tim KaineTimothy (Tim) Michael KaineTrump's pick to lead Pentagon glides through confirmation hearing Acosta defends Epstein deal, bucking calls for resignation Republican lawmakers on why they haven't read Mueller report: 'Tedious' and 'what's the point?' MORE (D-Va.) and Sherrod BrownSherrod Campbell BrownThe Hill's Morning Report - A raucous debate on race ends with Trump admonishment On The Money: Senators unload on Facebook cryptocurrency | Tech giants on defensive at antitrust hearing | Democrats ask Labor Department to investigate Amazon warehouses Hillicon Valley: Senators unload on Facebook cryptocurrency plan | Trump vows to 'take a look' at Google's ties to China | Google denies working with China's military | Tech execs on defensive at antitrust hearing | Bill would bar business with Huawei MORE (D-Ohio) easily won reelection, and voters in New Jersey decided to send Sen. Bob MenendezRobert (Bob) MenendezPompeo changes staff for Russia meeting after concerns raised about top negotiator's ties: report Dem senators demand GOP judicial group discloses donors Senate passes .5B border bill, setting up fight with House MORE back to Washington for another six-year term.

But the defeat in Texas comes after Tennessee, another potential pickup, was quickly taken out of reach for Democrats with Rep. Marsha BlackburnMarsha BlackburnSocial media summit highlights partisan approaches on tech Trump announces, endorses ambassador to Japan's Tennessee Senate bid Hillicon Valley: Trump rails against 'terrible bias' at White House social media summit | Twitter hit by hour-long outage | Google admits workers listen to smart device recordings MORE (R-Tenn.) defeating former Gov. Phil Bredesen (D) after holding a lead in the polls heading into Tuesday.

Democrats are still eyeing potential pick-ups in two western states with seats currently held by Republicans — Arizona and Nevada.

Rep. Kyrsten Sinema (D-Ariz.) had a slight lead over Rep. Martha McSallyMartha Elizabeth McSallyTrump angry more Republicans haven't defended his tweets: report Republicans scramble to contain Trump fallout On The Money: Senators unload on Facebook cryptocurrency | Tech giants on defensive at antitrust hearing | Democrats ask Labor Department to investigate Amazon warehouses MORE (R-Ariz.) heading into Tuesday as they battle to succeed retiring Sen. Jeff FlakeJeffrey (Jeff) Lane FlakeFlake urges Republicans to condemn 'vile and offensive' Trump tweets Flake responds to Trump, Jimmy Carter barbs: 'We need to stop trying to disqualify each other' Jeff Flake responds to Trump's 'greener pastures' dig on former GOP lawmakers MORE (R). If Sinema is victorious it would be the first time since 1988 that Arizonans have elected a Democrat to the Senate.

Meanwhile, Democrats held a lead among early voters in Nevada, where Democrats are feeling bullish about their ability to unseat Sen. Dean HellerDean Arthur HellerThis week: Barr back in hot seat over Mueller report Trump suggests Heller lost reelection bid because he was 'hostile' during 2016 presidential campaign Trump picks ex-oil lobbyist David Bernhardt for Interior secretary MORE (R-Nev.), the only Republican senator up for reelection in a state won by Democratic presidential nominee Hillary ClintonHillary Diane Rodham ClintonTrump thanks 'vicious young Socialist Congresswomen' for his poll numbers Will Trump's racist tweets backfire? Democrats fret over Trump cash machine MORE in 2016.

Updated at 12:54 a.m.