Trump expected to replace Mattis on Jan. 1 - U.S. official

WASHINGTON - 24 December 2018: U.S. President Donald Trump is expected to announce that Deputy Secretary of Defense Patrick Shanahan will take over from Jim Mattis as acting secretary of defense as of Jan., a senior U.S. administration official told Reuters.

Mattis resigned on Thursday over policy differences with Trump but said he would remain on the job until the end of February to ensure a smooth transition.