In conjunction with his time in Congress and before he was a presidential candidate, Lindsey Graham spent 33 years in the U.S. Air Force across three components — as an active-duty staff judge advocate, a South Carolina Air National Guard officer and a senior lawyer in the Air Force Reserve.

Graham, 71, died unexpectedly Saturday from an aortic dissection, according to a preliminary report from the Washington, D.C., Office of the Chief Medical Examiner. The South Carolina senator had returned hours earlier from a trip to Ukraine, where he sought to negotiate new sanctions against buyers of Russian oil.

In a Truth Social post Saturday, President Donald Trump called Graham “one of the greatest people and senators” he had ever known.

“He was always working and was a great American patriot,” Trump wrote.

Trump added later that the country had “lost a great man.”

“We lost a great person, a kind person, a very smart person … Everything for him was about work. It was about loving the country,” Trump said.

In a statement Sunday, Sen. Jack Reed, D-R.I., remembered Graham as a “polarizing” figure, but also as an intellectual who devoted himself to his causes.

“Theodore Roosevelt’s famous ‘Man in the Arena’ concept certainly applies to Senator Graham, who relished the dust, sweat, and challenges of public life,” Reed said in a statement. “One day, we’d be fiercely debating the Iraq war and the next day he’d be the lone Republican on the floor sticking up for a judicial nominee from Rhode Island. And in both instances, he’d bring his same keen intellect, high-level energy, and effectiveness to bear.”

Graham, a foreign policy hawk known for staunchly defending Israel and Ukraine, joined the Air Force in 1982 shortly after finishing law school at the University of South Carolina.

In the first two years of his career, he garnered national attention for uncovering problems with drug testing procedures at Brooks Air Force Base in San Antonio, Texas, that included the mishandling of samples and the discharge of innocent airmen from the service.

The effort was highlighted in a report by 60 Minutes in 1984 and earned then-Capt. Graham an Air Force Commendation Medal.

Graham then spent four years in Germany before leaving active duty in 1988 and returning home to join the South Carolina Air National Guard.

Two years later, Graham was activated for the 1990-91 Persian Gulf War to provide support for service members preparing for deployment at McEntire Air National Guard Base.

Graham continued to serve in the Air Force after he was elected to the U.S. House in 1994 and the U.S. Senate in 2002, although a 2015 analysis by The Washington Post found that from 1995 to 2005, he received credit for 108 hours of training, less than a day and a half per year.

Graham told the publication that he called the period his “wilderness years,” in which he struggled to find his place in the Reserves while working as a legislator. He was not paid during that period and only collected retirement points during that time.

Once he established himself in the U.S. Senate, however, Graham spent congressional breaks on short-term duty in Iraq and Afghanistan, where he worked on Rule of Law issues.

In addition to his Air Force Commendation Medal, Graham earned a Meritorious Service Medal for his work at Rhein-Main Air Base in Germany and was awarded a Bronze Star for service as a senior legal adviser in Operation Enduring Freedom.

Graham retired as a colonel from the Air Force Reserves in June 2015 just as he announced his candidacy for the 2016 Republican presidential nomination. He suspended that effort six months later.

Graham and his sister, Darline, were orphaned in 1977 following the deaths of their parents. In 1982, after he joined the Air Force, Graham formally adopted his sister, nine years his junior, to ensure that she had access to Tricare health care coverage and other military benefits.

On Monday, Trump proposed that Graham’s sister, Darline Graham Nordone, fill his seat through Jan. 3, 2027, the remainder of his term. Graham was running for reelection in November.

Air Force Chief of Staff Gen. Ken Wilsbach thanked Graham not only as a senator but “as an Airman.”

“I had the privilege to serve alongside him in combat, where he was a phenomenal officer and [judge advocate general]” wrote Wilsbach on X on Monday. “What an asset we had with a sitting member of Congress, who was an air-minded Senator … On behalf of all Airmen, we send condolences to the Graham family.”