Former President George W. Bush on Sunday mourned the death of Sen. Lindsey Graham, R-S.C., calling the longtime South Carolina Republican a knowledgeable lawmaker who grasped why American power abroad matters, as tributes poured in for the 71-year-old foreign policy hawk who died Saturday night after what his office described as a brief and sudden illness.

"Laura and I were saddened to wake up to the shocking news of Senator Lindsey Graham's death," Bush said in a joint statement with the former first lady. "He was a knowledgeable Senator who understood how the world works and how important America's international engagement is to resist tyranny."

The former president called Graham "a kind and funny man who loved our country and loved serving it," adding that South Carolina "was fortunate to have such a committed public servant in its corner. And I was fortunate to have known Lindsey Graham."

The tribute reflected a working relationship that spanned Bush's presidency and Graham's rise on Capitol Hill, from bipartisan immigration negotiations to Graham's role as a Judiciary Committee Republican during a period of contested detainee-policy fights.

Graham, first elected to the Senate in 2002, died Saturday evening. Emergency responders were dispatched to his Capitol Hill residence around 8:30 p.m. for a report of chest pains, and audio of the call referenced cardiac arrest. His office confirmed the death early Sunday and asked for privacy.

President Donald Trump, who golfed frequently with Graham and had turned to him for advice on foreign policy, called him "a true American Patriot" in a Truth Social post and ordered flags at the White House to be lowered to half-staff.

Graham had returned from Kyiv only days earlier, his 10th wartime visit, where he met with Ukrainian President Volodymyr Zelenskyy and announced that he and a bipartisan group of senators had reached a deal with the White House to move his long-stalled Russia sanctions bill.

Zelenskyy on Sunday called him a "true defender of freedom," and Israeli Prime Minister Benjamin Netanyahu said Graham "devoted his life to defending America, strengthening our alliance and standing up for the free world."

Under South Carolina law, Republican Gov. Henry McMaster will appoint a temporary replacement to serve until Jan. 3 following the next general election.

Because Graham had already secured the GOP nomination for a fifth term, state officials also must run a special primary. Election officials said filing is expected to open July 21, with a primary by Aug. 11 and a possible runoff two weeks later.

The winner will face Democratic nominee Annie Andrews in November.

Graham, chairman of the Senate Budget Committee, last voted in the chamber on June 24. The Senate is scheduled to return Monday.