ALSO SEE: Lindsey Graham, Pivotal Republican Senator, Dies Suddenly at 71

He died of “a brief and sudden illness” on Saturday evening, his office said. Over more than two decades in the Senate, he consistently pushed for the use of U.S. military power overseas.

Senator Lindsey Graham, a South Carolina Republican and stalwart ally of President Trump who was a forceful advocate for an interventionist U.S. foreign policy, died on Saturday evening. He was 71.

He died of “a brief and sudden illness,” his office said in a statement early Sunday. No further details were provided about where he died or the cause. After recently returning from a trip to Ukraine, Mr. Graham had been scheduled to appear on NBC’s “Meet the Press” on Sunday morning.

Mr. Graham was first elected to the U.S. House of Representatives in 1994, before winning his Senate seat in 2002. Last month, he fended off five challengers to win the Republican primary in his bid for a fifth term.

Mr. Trump offered his condolences on social media early Sunday, calling Mr. Graham “one of the greatest people and Senators I have ever known.”

“He was always working, and was a true American Patriot,” Mr. Trump added. “Lindsey will be greatly missed!!!”

Gov. Henry McMaster of South Carolina, a Republican, can immediately appoint a temporary replacement to fill Mr. Graham’s Senate seat. Mr. Graham was set to face Annie Andrews, a Democrat and a pediatrician, in the general election in November.