US President Donald Trump on Sunday reacted to the sudden death of Senator Lindsey Graham, recounting in an interview with NBC's Meet the Press what he said may have been one of the senator's final phone calls.

"He's a tough one to lose. He was great. He was unique in every way, actually," Trump said.

According to Trump, Graham called him in the early evening after returning to Washington from a trip to Ukraine.

"He called and he said, 'We're all set for the Save America Act.' He was pushing the Save America Act like crazy," Trump recalled.

"He got back, said he just landed from Ukraine. I said, 'That's a long trip to make.' He sounded a little tired, but perfect, but a little bit tired."

Trump said Graham told him that he was tired following the journey but remained focused on advancing the legislation.

"I said, 'Well, we're going to get it done, Lindsey. We're going to get it done. I'll see you soon.' We thought we might even meet today. And then that was it," the President said.

"It couldn't have been much longer. It could have been his last call. I don't know exactly."

Trump said he received a message at approximately 1:00 a.m. from a member of Graham's office informing him that the senator had passed away.

"I said, 'You guys, I just can't believe it.' He was like a member of the family to me. It's very tough, actually."

Asked whether Graham had indicated during their conversation that he was feeling unwell, Trump said the senator had only complained of fatigue following his long trip.

"No, he said he's a little tired. It was a long trip, many hours. And he had just gotten back," Trump told *Meet the Press*.

"He told me, Kristen, he said, 'You know, I feel good, but I'm tired.' He was fine."

Trump added: "I knew him well. He would let you know if he wasn't feeling well."

Reflecting on Graham's political career, Trump described him as a skilled politician who was able to work with members of both parties.

"He was an amazing advocate. He was - I don't know how you find anybody like him," Trump said.

"He was a great, like, a gauge, a temperature gauge of the Senate. He was somebody that most Democrats liked. Some didn't, but most Democrats liked. And just about all of the Republicans liked Lindsey."

Trump also recalled his changing relationship with Graham, who initially competed against him during the 2015 presidential campaign before becoming one of his closest allies.

"I got to know Lindsey during the campaign," Trump said. "He was tough."

"He appreciated it. He respected it. And we sort of got a little bit friendly, and just the friendship grew. It just grew."

Asked to recall his final words to Graham, Trump said: "I said, 'We'll see you soon. Come over anytime you want.'"

"He came into the White House a lot because I liked him," Trump added.

Trump also pointed to Graham's role during the confirmation process of Supreme Court Justice Brett Kavanaugh as a central part of the senator's legacy.

"He's got so many legacies, but one of the legacies is a Supreme Court justice who's excellent named Brett Kavanaugh. That's one of the legacies. That's a big legacy," Trump said.

"He was a great politician. He really was. He got along with a lot of people that you wouldn't think of. He was somebody that loved our country, and he fought very hard for the country."

Trump said Graham had told him during their final conversation that he was scheduled to appear on *Meet the Press* the following morning.

"He told me, 'I'm doing Meet the Press.' Can you believe it? He said, 'Here I am doing Meet the Press,'" Trump recalled.

"But I said, 'Just relax and take it easy, Lindsey. You just got back from a long trip.'"

"I thought he was just going to live forever," Trump concluded, "and it didn't work out that way."