A spokeswoman for Defense Secretary James Mattis said following the Sunday announcement that he will leave his position two months earlier than planned that he “remains focused on the defense of the nation.” 

“The Secretary of Defense serves at the pleasure of the President. #SecDef Mattis will work with Deputy Shanahan and department leadership to ensure the #DOD remains focused on the defense of the nation during this transition,” Dana White, the assistant to the secretary of Defense for public affairs, wrote in a tweet.

The Secretary of Defense serves at the pleasure of the President. #SecDef Mattis will work with Deputy Shanahan and department leadership to ensure the #DOD remains focused on the defense of the nation during this transition.

— Dana W. White – DOD (@ChiefPentSpox) December 23, 2018

{mosads}White’s statement came after President Trump announced Sunday that Mattis will leave his position on Jan. 1, two months before he previously planned to depart.

Trump wrote in a tweet that Mattis’s deputy, Patrick Shanahan, will replace Mattis and serve as acting chief of the Pentagon.

Mattis last week resigned from his position after Trump announced he would withdraw U.S. troops from Syria.

In his resignation letter, Mattis wrote that Trump deserves a Defense secretary “whose views are better aligned with yours” and said he was concerned with how Trump treated U.S. allies.

Trump wrote in a tweet Saturday that allies are “very important-but not when they take advantage of U.S.”