President Donald Trump on Sunday ordered American flags nationwide to be flown at half-staff through Saturday evening in honor of former Sen. Lindsey Graham, calling the South Carolina Republican "a dear friend" and "a truly great man."

Graham, one of Trump's closest allies in the Senate, died suddenly Saturday.

The president spent much of Sunday paying tribute to Graham in television interviews and on social media before issuing a proclamation directing flags to remain at half-staff until 6 p.m. Saturday.

"In honor of the remarkable life and achievements of Senator Lindsey Graham, a dear friend of mine, and a truly great man, who achieved so much for our Country, and his beloved Home State of South Carolina, I am ordering all American Flags throughout the United States lowered to Half Mast until Saturday evening at 6 P.M.," Trump wrote. "GOD BLESS YOU LINDSEY!"