President Trump announced on Sunday that Defense Secretary Jim Mattis will now leave his post on Jan. 1, tweeting that deputy Pentagon chief Patrick Shanahan will take over as acting secretary to cover the accelerated departure, the AP reports. The move comes just three days after Mattis resigned in protest over Trump's decision to pull all US troops out of Syria, and delivered a blistering letter to the president that roiled Washington and reportedly angered the White House. Mattis originally said he would stay through February to ensure an orderly transition. A source says the fallout of his decision to leave—including the shock and dismay expressed on Capitol Hill—annoyed Trump and led him to push Mattis out sooner than planned, per CNN.
Lt. Col. Joseph Buccino, a spokesman for Shanahan, says the former Boeing executive will accept the appointment as acting secretary. "Deputy Secretary will continue to serve as directed by the president, and the Department of Defense will remain focused on the defense of the nation," Buccino said on Sunday. While Mattis' resignation followed Trump's announcement that he would soon pull all of the approximately 2,000 US troops out of Syria, officials say the resignation was the result of an accumulation of disagreements. In a stunning resignation letter, Mattis made clear he did not see eye to eye with a president who has expressed disdain for NATO and doubts about keeping troops in Asia. (Trump says he gave Mattis "a second chance.")