Washington — President Trump endorsed Texas Attorney General Ken Paxton on Tuesday in the state’s upcoming Senate runoff, seeking to bring to an end a costly contest just a week ahead of the runoff date.  

“Ken is a true MAGA Warrior who has ALWAYS delivered for Texas, and will continue to do so in the United States Senate,” Mr. Trump said in a post on Truth Social. 

Paxton is heading to a May 26 runoff against four-term Sen. John Cornyn after neither secured 50% of the vote in the March 3 primary election. Cornyn won about 42% of the vote, while Paxton had almost 41% — ultimately a margin of about 26,000. 

Early voting started Monday in the runoff. 

Mr. Trump initially said in March that he planned to endorse a candidate in the race “soon,” adding that he would tell the other candidate to drop out of the race. He said at the time that the GOP primary race in Texas “cannot, for the good of the Party, and our Country, itself, be allowed to go on any longer.” But as weeks went by without an endorsement, the candidates have endured a costly extension of the primary, with the president’s input appearing increasingly unlikely. 

The possibility of the endorsement has weighed heavy on the race between Paxton, a staunch ally of the president, and Cornyn, who Mr. Trump has previously criticized for questioning whether he could win a general election in 2024. And although Cornyn has worked to mend his  relationship with the president and has become a vocal supporter of Mr. Trump’s second–term agenda, the dynamic made for a messy primary fight. 

An election bill known as the SAVE America Act came front and center in the fight in recent months. Paxton said he would consider dropping out of the race if Senate Republicans passed the legislation, which Mr. Trump has made his top priority in Congress. Then Cornyn reversed his position on the filibuster, backing changes to the Senate’s 60-vote threshold to allow for the legislation’s passage. 

The endorsement comes despite the wishes of Senate Republicans, who are eager to hold onto the seat in November and who see Cornyn as a better candidate to take on Texas state Rep. James Talarico, the moderate Democratic nominee, in a general election. 

Senate GOP leaders backed Cornyn long before Mr. Trump weighed in on the race. And Senate Majority Leader John Thune has told reporters that Cornyn is well positioned to “win the runoff.” He said in March that if the president endorses early, it would save “everybody a lot of money.”