Polls have closed across most of Texas, where the results of bruising Democratic and Republican nominating contests on Tuesday for the U.S. Senate will test the divides roiling each party as the midterm elections officially kick off.

Voters in Texas, North Carolina and Arkansas cast the first ballots of the campaign to decide which party controls the U.S. Congress during President Donald Trump’s last two years in office.

The results of the vote will begin to set the stage for November’s general election, when all 435 seats in the U.S. House of Representatives and one-third of the Senate’s 100 seats will be at stake.

The elections take place days after the U.S. attacked Iran, a move that some White House aides privately worry could pose political risks for Trump and Republicans at a time when voters have made it clear they are more concerned with domestic issues, including affordability and immigration.

The Texas Senate election headlined the day’s voting, with both parties embroiled in fiercely contested nominating campaigns that shattered spending records for a Senate primary.

In North Carolina, voters were choosing nominees for a marquee Senate race that could determine the chamber’s majority. While most polls closed at 7:30 p.m. ET (0030 GMT), one location remained open for an extra hour after a technical problem, delaying the release of statewide results, according to the state elections board.

November’s battle for the U.S. House of Representatives will be particularly hard-fought, with Democrats needing to flip only three Republican-held seats to capture a majority in the chamber. Democrats face longer odds in winning the Senate.

Trump’s approval ratings have fallen, and the president’s party typically loses seats in midterm elections. A Democratic majority in either chamber could block much of Trump’s legislative agenda and open damaging investigations into his administration.

Texas Senate Race Exposes Tensions in Both Parties

In Texas, incumbent Republican John Cornyn, an establishment conservative who has served more than two decades in the Senate, has been locked in a close race for the party’s nomination with Texas Attorney General Ken Paxton, a firebrand ally of Trump who has remained popular with the president’s MAGA base despite a multitude of scandals.

Cornyn has argued that a Paxton victory would turn a safe Republican seat into a competitive race that could imperil the party’s slim Senate majority, while Paxton has dismissed Cornyn as out of touch with the state’s voters.

Both candidates have touted their support for Trump, including backing the military strikes in Iran. The president has not made a formal endorsement.

Senate Republican leadership has backed Cornyn, whose allies outspent Paxton’s side $69 million to $4 million on advertising, according to the tracking firm AdImpact.

With another far-right conservative, U.S. Representative Wesley Hunt, also running, the contest is likely to advance to a runoff election in May between the top two finishers.

On the Democratic side, James Talarico, a state representative who has put his Christian faith at the center of his campaign and made explicit appeals to Republican voters, is in a neck-and-neck race with U.S. Representative Jasmine Crockett, whose fiery denunciations of Trump have gained her a national following.

Democrats have long harbored hopes of turning Texas blue, but the party has not won a statewide race since 1994. Nevertheless, party leaders argue Paxton – who has survived an impeachment by Republican lawmakers, a securities fraud indictment and a messy divorce – could prove vulnerable in November.

Analysts said Paxton would still be the favorite given Texas’ conservative electorate.

“Ken Paxton is still a Republican in a very Republican state that’s got a turnout machine that understands how to win elections,” said Brandon Rottinghaus, a University of Houston political science professor.

A judge ordered polls in Dallas County to remain open for an extra two hours, until 9 p.m. local time (0200 GMT), after a change in voting procedure left many voters confused about their polling locations, Decision Desk HQ reported.

New Maps Scramble Races

In North Carolina, Republican Thom Tillis’ impending retirement has created an open seat in a swing state.

Democrats hope former Democratic Governor Roy Cooper, who faces token intraparty opposition, can flip the seat in November. The popular Cooper has won statewide six times.

Michael Whatley, a former Republican National Committee chairman who boasts Trump’s endorsement, was the Republican frontrunner going into Election Day.

Tuesday’s contests will also mark the first time that new congressional maps are used in Texas and North Carolina, after Republican lawmakers last year redrew the states’ U.S. House district lines at Trump’s behest to try to gain more Republican seats, igniting a nationwide redistricting fight.

The new Texas map already prompted two Democratic incumbents whose districts were eliminated to retire. In the Houston area, two sitting Democratic congress members, Al Green and Christian Menefee, are facing each other after the new map dismantled Green’s previous seat.

Republican Tony Gonzales, who was already facing a stiff challenge from a conservative YouTuber, also is in danger of losing his seat following allegations that he had a relationship with a female staffer who later died by suicide. He has denied wrongdoing but has faced bipartisan calls to resign.

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(Reporting by Joseph Ax; Additional reporting by Nolan D. McCaskill; editing by Paul Thomasch and Deepa Babington)