WASHINGTON (AP) — Sen. Lindsey Graham, one of President Donald Trump’s closest allies in Congress who traveled the globe to advocate for a more aggressive U.S. foreign policy, died after a rupture in his aorta, according to a preliminary medical examiner finding shared by his office.

The rupture was related to the hardening of Graham’s arteries. An official cause of death will be disclosed after toxicological and microscopic testing.

Graham, a prominent South Carolina Republican and former Air Force lawyer who served in Congress for more than three decades, had turned 71 years old just two days before dying on Saturday night. His office had originally said he had suffered from a “brief and sudden illness.”

Trump, who talked to Graham frequently, said he was “like a member of the family. It’s very tough.” He said on NBC’s ”Meet the Press” that Graham had called him on Saturday night after returning from a trip to Ukraine and “sounded a little bit tired, but perfect.” The president ordered that flags across the country be flown at half-staff until next Saturday evening.

A noted foreign policy hawk, Graham was one of the most influential figures in Washington on international affairs and he advised Trump on matters such as the Iran war and Russia. On Friday, Graham had announced an agreement with the Trump administration to move forward on a package of Russia sanctions.

As chairman of the Senate Budget Committee, Graham also had a central role during Trump’s second term as Republicans pushed major legislation on party-line votes while holding a narrow 53-47 majority in the chamber.

Under South Carolina law, Republican Gov. Henry McMaster will appoint a temporary replacement for Graham, who was seeking a fifth term in November. A new nominee will be selected in a special primary, which is required to be held within weeks of a vacancy. The winner of November’s general election will start a full six-year term in January.

Graham had a close, complicated relationship with Trump
Graham, elected to the Senate in 2002 after serving in the House, long promoted a policy of robust U.S. military interventionism and strong national defense that in later years would put him at odds with the growing isolationist wing of his party.

Over time, Graham became well-known for his close ties with Trump, whom the senator briefly ran against for the presidential nomination in 2016.

Their relationship would begin on a rough note, with Graham calling the then-New York businessman “unfit for office.” Graham used a profanity to describe Trump after Trump made disparaging comments about Arizona Republican John McCain, Graham’s best friend in the Senate and a Vietnam War veteran. McCain and Graham, along with Sen. Joe Lieberman, I-Conn., were known as the “Three Amigos” and frequently traveled together to promote their foreign policy views around the globe.

During a campaign rally in South Carolina, Trump read out Graham’s personal cellphone number and continued to belittle him throughout the 2016 race as Graham made it clear he would not support Trump.

Graham, however, shifted significantly once Trump won the White House and emerged as one of Trump’s top allies — speaking with him frequently and becoming a regular presence on the golf course alongside the president — even as McCain remained a critic.

In a 2018 interview with The Associated Press, Graham explained his pivot by saying McCain taught him that the country must move forward after elections and that meant “you have an obligation” to help the president. McCain ran twice for the White House.

“And I’ve tried to be helpful where I could because I think he needs all the help he can get,” Graham said of Trump. “You can be a better critic when people understand that you’re trying to help them be successful.”

Graham was a prominent defender of Trump during the president’s two first-term impeachments — a reversal from Graham’s role as a House prosecutor during Democratic President Bill Clinton’s impeachment in 1998, when he urged senators not to make up their minds before listening to all of the arguments. Both Trump and Clinton were eventually acquitted.

Graham appeared to break with Trump after the Jan. 6, 2021, attack on the Capitol, saying in a dramatic speech on the Senate floor that night, “Count me out. Enough is enough.” But the senator soon returned to Trump’s side and the two remained close during Trump’s second term.

Foreign policy was a focus for Graham
Graham had just been in Ukraine to meet with Ukrainian President Volodymyr Zelenskyy, who said the senator visited his country 10 times during the years since Russia invaded in February 2022. “Lindsey was a true defender of freedom and the values that make our world safer,” Zelenskyy said.

He was also one of the chief backers of Trump’s war in Iran, having advocated for years for direct confrontation between Washington and Tehran. Graham continued to defend Trump this summer even as many of fellow Republicans questioned a tentative June ceasefire agreement that they worried could send billions of dollars to Iran.

“I’d rather try diplomacy than take it off the table,” Graham said of Trump’s memorandum of understanding with Tehran.

Graham’s travels made him a familiar face to dozens of world leaders.

Israeli Prime Minister Benjamin Netanyahu said Graham understood that the security of Israel and the United States was inseparable.

“Israel has lost one of its greatest friends. America has lost a great patriot. I have lost a beloved friend,” Netanyahu said.

Graham led both the Senate Budget and Judiciary committees
As Budget Committee chairman, Graham helped oversee a Senate procedure that allowed Republicans to pass significant policies such as last year’s tax law without the threat of a Democratic filibuster.

He had previously led the Senate Judiciary Committee when Republicans confirmed Amy Coney Barrett to the Supreme Court in 2020. The senator was in line to regain that gavel if the party kept its majority after the midterm elections and had pledged to confirm “as many conservative judges as possible.”

Graham was a key player in the Senate’s efforts to craft a massive immigration overhaul in 2013 as a member of a bipartisan group. The legislation passed the Senate with 68 votes but was never taken up by the House, so it did not become law.

Graham’s views on immigration, particularly an endorsement of a path to citizenship for people in the U.S. without legal status, put him at odds with some Republican factions.

Illinois Sen. Dick Durbin, a Democrat who was his ally on that issue, said Graham was “part of every important policy issue and an indispensable player” in bipartisan negotiations.

An ‘irreplaceable’ force in the Senate
Graham often worked across the aisle, even as he remained fiercely loyal to Trump. Virginia Sen. Mark Warner, a Democrat, said in a statement that “personal relationships often mattered more to him than the political disagreements of the day.”

Sen. Richard Blumenthal, D-Conn., said Graham was “over the moon” with the Russian sanctions deal announced Friday. “The last thing in the world I would have guessed was that he was sick or ill or in any way vulnerable,” Blumenthal said.

Jaime Harrison, a former national and state Democratic Party chairman who unsuccessfully ran against Graham in 2020, said that even during their “fiercest political battles” the two men “could still share a conversation, a laugh, and a mutual respect for South Carolina.”

Graham was unique in the Senate for his influence not only on Trump, but also with his fellow Republicans who were aware of his ability to sometimes move the president’s thinking. He was also known for his sense of humor, often deployed to diffuse tensions.

Wyoming Sen. John Barrasso, the second-ranking Republican, said Graham will be missed for his “quick wit and infectious laughter.”

McMaster said in a statement that Graham was “irreplaceable.” Former Republican President George W. Bush said Graham “understood how the world works” and “was a kind and funny man who loved our country and loved serving it.”

Graham often spoke about his humble roots, growing up in the back of a South Carolina bar and helping to raise his sister, Darline, after his parents died at a young age. Graham was not married and did not have children.

Special election to replace Graham could be within weeks
Graham won 57% of the GOP vote in South Carolina’s primary in June and was up against Democrat Annie Andrews, a pediatrician, and several minor party and independent candidates in November.

His death will likely prompt a scramble to fill a rare open Senate seat.

A number of Republican names began circulating as possible replacements to serve out the rest of Graham’s term, including three candidates who fell short for the party’s nomination for governor this year — Rep. Nancy Mace, Rep. Ralph Norman and Lt. Gov. Pamela Evette.

Also in the mix is Rep. Russell Fry, who was elected to the House in 2022.