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 HeitkampSusan Collins set to play pivotal role in impeachment drama Pro-trade group launches media buy as Trump and Democrats near deal on new NAFTA The Hill's Morning Report — Biden steadies in third debate as top tier remains the same MORE (N.D.), Claire McCaskillClaire Conner McCaskillHow Citizens United altered America's political landscape #MidnightMoscowMitch trends amid criticism of McConnell's proposed impeachment trial rules The most expensive congressional races of the last decade MORE (Mo.) and Bill NelsonClarence (Bill) William NelsonThe most expensive congressional races of the last decade Lobbying world Bottom Line MORE (Fla.).

The red-state Democratic losses came after Republicans avoided a major upset in Texas, where Rep. Beto O'RourkeBeto O'RourkeVeronica Escobar to give Spanish-language response to Trump State of the Union address Biden calls for revoking key online legal protection Trump mocks Booker over suspended presidential campaign MORE (D) shot into an early lead but was ultimately unable to overcome Sen. Ted CruzRafael (Ted) Edward CruzRepublicans show little enthusiasm for impeachment witness swap Texas House special election to gauge suburban mood Texas Democrats roll out plan to win state House in November 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.

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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) ManchinThe Hill's Morning Report - Report of Bolton tell-all manuscript roils Trump defense Democrats Manchin, Jones signal they're undecided on Trump removal vote Schiff sparks blowback with head on a 'pike' line 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 KaineThis week: Senate barrels toward showdown on impeachment witnesses Kaine: GOP senators should 'at least' treat Trump trial with seriousness of traffic court Senate Dems to Pompeo: Comments about NPR reporter 'insulting and contemptuous' MORE (D-Va.) and Sherrod BrownSherrod Campbell BrownSchiff sparks blowback with head on a 'pike' line Sunday shows - All eyes on Senate impeachment trial Senate Democrat: 'Fine' to hear from Hunter Biden MORE (D-Ohio) easily won reelection, and voters in New Jersey decided to send Sen. Bob MenendezRobert (Bob) MenendezMedia's selective outrage exposed in McSally-Raju kerfuffle Dem senators say Iran threat to embassies not mentioned in intelligence briefing Overnight Defense: Iran crisis eases as Trump says Tehran 'standing down' | Dems unconvinced on evidence behind Soleimani strike | House sets Thursday vote on Iran war powers 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 BlackburnTaylor Swift on publicist's Trump warning before political post: 'F--- that, I don't care' GOP cries boredom in attack on impeachment case Marsha Blackburn shares what book she's reading during Trump Senate trial 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 McSallyProgressive group targeting vulnerable GOP senators on impeachment witnesses Senate Republicans face pivotal moment on impeachment witnesses Democrats feel political momentum swinging to them on impeachment MORE (R-Ariz.) heading into Tuesday as they battle to succeed retiring Sen. Jeff FlakeJeffrey (Jeff) Lane FlakeThe Hill's 12:30 Report: House managers to begin opening arguments on day two Flake: Republicans don't speak out against Trump 'because they want to keep their jobs' GOP senator calls CNN reporter a 'liberal hack' when asked about Parnas materials 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 HellerLobbying World Democrats spend big to put Senate in play This week: Barr back in hot seat over Mueller report MORE (R-Nev.), the only Republican senator up for reelection in a state won by Democratic presidential nominee Hillary ClintonHillary Diane Rodham ClintonDershowitz: Bolton allegations would not constitute impeachable offense Hillicon Valley — Presented by Philip Morris International — NFL social media accounts hacked | Dem questions border chief over controversial Facebook group | Clinton says Zuckerberg has 'authoritarian' views Clinton on Sanders comments: 'I wasn't thinking about the election' MORE in 2016.

Updated at 12:54 a.m.