James Mattis

Defense Secretary James Mattis released a farewell message to all employees on Monday, in the waning hours of his job as Pentagon chief.

"I am confident that each of you remains undistracted from our sworn mission to support and defend the Constitution while protecting our way of life," he wrote.

He said that the Pentagon is at its best "when the times are most difficult," and told them to "keep the faith in our country and hold fast, alongside our allies, aligned against our foes."

Updated at 10:45 p.m. ET

Defense Secretary Jim Mattis, a living Marine Corps legend who made history by securing special permission from Congress to lead the Pentagon, is stepping down after a slow freeze-out by President Trump.

Drift between the two men reached a point at which Mattis objected so strongly to the president's policy choices that he opted to resign rather than go along.

During a State of the Nation Address last year, the President of the Philippines Rodrigo Duterte called on the U.S. "Give us back those Balangiga bells," said Duterte. "They are ours. They belong to the Philippines. They are part of our national heritage."