Charleston, S.C. -- U.S. Sen. Lindsey Graham on Friday endorsed former  Florida Gov. Jeb Bush for the Republican nomination for president.

Graham, who ended his bid for the White House in December, said Bush is the only candidate in the race who can defend America.

"I have concluded without any hesitation or any doubt that Jeb Bush is ready on day one to be commander in chief," Graham said in a hastily called news conference. "Last night (in the Republican debate) he said, 'I will have your backs.' I believe he will. Last night he explained in the best possible terms why we need partners to win a war we can’t afford to lose."

The move, while significant in this early voting state, was not unexpected. Since he dropped out, much of Graham's top backers moved to Bush's camp, including former Ambassador to Canada David Wilkins. Many of the state's top GOP donors, too, migrated to Bush, such as Florence Dr. Eddie Floyd and Bob Royall, former ambassador to Tanzania.

"Lindsey Graham is an extraordinary person," Bush said. "He views his job to forge solutions to problems, rather than try to tear things down."

Graham's expertise on national security is unparalleled, he said.

"Lindsey Graham is by far and away recognized as the strongest policy oriented national defense senator, the most consistent supporter of a strong national defense in the country, period, over and out," Bush said.