Senate Minority Whip John Thune (R-S.D.) is endorsing former President Trump for president in 2024, a source familiar confirmed to The Hill.

Thune’s support marks a high-profile win for Trump, from the No. 2 Republican in the Senate, who is seen as a serious legislator and a possible successor to Senate Minority Leader Mitch McConnell (R-Ky.).

Thune spoke with Trump by phone on Saturday night after Trump won South Carolina’s primary, the source confirmed.

Thune has at times been critical of Trump and has broken with him on several key votes. This weekend’s endorsement only underscores Trump’s strong grip on the party.

Last month, Thune said he would support whoever became the ultimate GOP nominee, adding that Trump seems to be on a strong path toward victory in upcoming primaries.

“I’m interested in what the people are saying, and voters are breaking heavily in his favor. He’s in a commanding position, and I’ve said all along I’ll support the nominee,” Thune said last month. “If he’s the nominee, I’ll do what I can to help the team win the presidency and the Senate and put an end to the Biden/Schumer agenda.”

In recent weeks, Republican senators have faced growing pressure to endorse the party front-runner.

Two other possible McConnell successors have endorsed Trump: Sen. John Barrasso (R-Wyo.), who backed Trump early, and Sen. John Cornyn (R-Texas), who announced his endorsement after Trump won the New Hampshire primary.

Sen. Tim Scott (R-S.C.) announced his endorsement for Trump after he suspended his own campaign for president. Some had remained hopeful that Scott would endorse Republican presidential candidate Nikki Haley, who first appointed him to the Senate when she was governor of South Carolina.

Haley remains the last opponent challenging Trump in the presidential primary. On Saturday, Trump won the primary by 20 points, with approximately 60 percent of the vote, compared with Haley’s nearly 40 percent, according to The Hill/Decision Desk HQ’s election results tracker.

Al Weaver contributed. Updated at 10:05 p.m.