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 HeitkampOn The Money: Stocks sink on Trump tariff threat | GOP caught off guard by new trade turmoil | Federal deficit grew 38 percent this fiscal year | Banks avoid taking position in Trump, Dem subpoena fight Fight over Trump's new NAFTA hits key stretch Former senators launching effort to help Dems win rural votes MORE (N.D.), Claire McCaskillClaire Conner McCaskillLobbying world Big Dem names show little interest in Senate Gillibrand, Grassley reintroduce campus sexual assault bill MORE (Mo.) and Bill NelsonClarence (Bill) William NelsonRepublicans amp up attacks on Tlaib's Holocaust comments The muscle for digital payment Rubio says hackers penetrated Florida elections systems MORE (Fla.).

The red-state Democratic losses came after Republicans avoided a major upset in Texas, where Rep. Beto O'RourkeBeto O'RourkeButtiegieg backs NFL players' right to protest during anthem: I 'put my life on the line to defend' that Overnight Energy: Democrats ask if EPA chief misled on vehicle emissions | Dem senators want NBC debate focused on climate change | 2020 hopeful John Delaney unveils T climate plan CNN's O'Rourke town hall finishes behind Fox News, MSNBC MORE (D) shot into an early lead but was ultimately unable to overcome Sen. Ted CruzRafael (Ted) Edward CruzThe Hill's Morning Report — After contentious week, Trump heads for Japan Senate GOP votes to permanently ban earmarks Jim Carrey fires back at 'Joe McCarthy wanna-be' Cruz 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) ManchinThe Hill's Morning Report - Trump says no legislation until Dems end probes Senate panel approves Interior nominee over objections from Democrats Labor head warns of 'frightening uptick' in black lung disease among miners 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 KaineOvernight Defense: Details on Senate's 0B defense bill | Bill rejects Trump plan to skirt budget caps | Backfills money for border wall | Defense chief says more troops could head to Mideast Dem senator plans amendment to restrict military action against Iran Overnight Defense: Iran worries dominate foreign policy talk | Pentagon reportedly to send WH plans for 10K troops in Mideast | Democrats warn Trump may push through Saudi arms sale | Lawmakers blast new Pentagon policy on sharing info MORE (D-Va.) and Sherrod BrownSherrod Campbell BrownOn The Money: Judge upholds House subpoena for Trump financial records | Trump vows to appeal ruling by 'Obama-appointed judge' | Canada, Mexico lift retaliatory tariffs on US | IRS audit rate falls Lawmakers grapple with the future of America's workforce The Hill's Morning Report - Presented by Pass USMCA Coalition - Restrictive state abortion laws ignite fiery 2020 debate MORE (D-Ohio) easily won reelection, and voters in New Jersey decided to send Sen. Bob MenendezRobert (Bob) MenendezEnding the Cyprus arms embargo will increase tensions in the Eastern Mediterranean We can accelerate a cure for Alzheimer's The Hill's 12:30 Report: Manafort sentenced to total of 7.5 years in prison 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 BlackburnOn The Money: Senate passes disaster aid bill after deal with Trump | Trump to offer B aid package for farmers | House votes to boost retirement savings | Study says new tariffs to double costs for consumers Senate passes disaster aid bill after deal with Trump Hillicon Valley: Google delays cutting off Huawei | GOP senators split over breaking up big tech | Report finds DNC lagging behind RNC on cybersecurity 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 McSallyOn The Money: Senate passes disaster aid bill after deal with Trump | Trump to offer B aid package for farmers | House votes to boost retirement savings | Study says new tariffs to double costs for consumers Senate passes disaster aid bill after deal with Trump Senate defense bill would make military sexual harassment standalone crime MORE (R-Ariz.) heading into Tuesday as they battle to succeed retiring Sen. Jeff FlakeJeffrey (Jeff) Lane FlakeSen. Coons examines Amazon's privacy and data security practices for Alexa devices Oil companies join blitz for carbon tax The Hill's Morning Report - White House, Congress: Urgency of now around budget 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 ClintonFrustration boils over with Senate's 'legislative graveyard' Poll: Nearly half of Clinton's former supporters back Biden Harris readies a Phase 2 as she seeks to rejuvenate campaign MORE in 2016.

Updated at 12:54 a.m.