Sen. Lindsey Graham (R-SC) died Saturday after a sudden illness, according to a statement from his office. He was 71.

“Senator Lindsey Graham, one of the greatest people and Senators I have ever known, is dead! He was always working, and was a true American Patriot. Lindsey will be greatly missed!!!” President Donald Trump wrote Sunday on Truth Social, adding that Graham’s death was “so sad.”

“He was a strong advocate for the United States and a strong ally to freedom-loving countries across the globe,” Senate Majority Leader John Thune (R-SD) wrote on X. “He believed in the might of America to achieve good in the world and dedicated his life to advancing that cause.”

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Graham held aggressive foreign policy positions, arguing in outspoken terms for military escalation against Iran and introducing sanctions legislation against Russia.

The former Air Force lawyer was elected to the House of Representatives in 1994 and the Senate in 2002. In 2015, Graham briefly ran for president in the nomination race that would eventually bring Trump onto the GOP ticket and then into the White House. Despite his early criticism of Trump, whom he described as “unfit” to be president, Graham became an influential member of the president’s inner circle.

South Carolina’s Republican Gov. Henry McMaster will appoint a replacement to serve out the remainder of Graham’s current term, which ends Jan. 3. The Palmetto State’s GOP has until Aug. 11 to hold a special primary to find a replacement candidate for Graham, who was running for reelection.