President Donald Trump offered condolences Sunday following the death of U.S. Sen. Lindsey Graham, calling the South Carolina Republican “one of the greatest people and Senators I have ever known.”

“Senator Lindsey Graham, one of the greatest people and Senators I have ever known, is dead! He was always working, and was a true American Patriot. Lindsey will be greatly missed!!!” Trump wrote in a post on Truth Social.

Graham remained one of Trump’s closest congressional allies during the president’s second term, frequently advising him on national security and foreign policy. The senator advocated a tougher approach toward Iran and Russia and worked to build bipartisan support for legislation imposing sanctions and tariffs on countries that continued doing business with Moscow during its war against Ukraine.

Their alliance was not without disagreements. Graham criticized Trump’s decision at the beginning of his second term to pardon people convicted in connection with the Jan. 6, 2021, attack on the U.S. Capitol, saying clemency for those who assaulted police officers sent the wrong message.

Still, Graham generally remained a prominent defender of Trump and an influential supporter of the administration’s foreign policy agenda.