Holed up in the White House over a government shutdown, and seething from a week of poor headlines, President Donald Trump gave himself an early Christmas present: revenge. During his Sunday tweet-storm, he took a brief sojourn from border-security to announce that he was naming deputy defense secretary Patrick Shanahan as acting successor to Jim Mattis, effectively expediting Mattis’s ouster.

Just days ago, Trump tweeted that General Mattis’ “retirement” would arrive “with distinction, at the end of February,” despite Mattis technically resigning in response to Trump’s unilateral decision to withdraw American forces in Syria. The New York Times reports the president “did not understand just how forceful a rejection of his strategy Mr. Mattis had issued” at the time, and only became aware of the rebuke after days of negative news coverage.

For Mattis, who was constantly referred to as part of the “axis of adults” reigning in a madcap president, Trump’s abrupt decision on Syria was the last straw. In his resignation letter, he emphasized his belief in the importance of maintaining strategic alliances—a fairly accepted concept in the national security establishment—and poignantly said that he believes the president “has a right” to a defense secretary whose views mesh with Trump’s own.

The president’s mood on Mattis had started to turn by Saturday.

In his resignation letter, Mattis said he would stay on through the end of his tenure, presumably to help ensure an orderly transition atop the nation’s entire military apparatus. Trump, naturally, was unmoved by such concerns. The Trump administration—battling a weakening economy, a government shutdown, and a handful of precarious foreign policy matters —is now served by an acting attorney general, acting chief-of-staff, and acting secretary of defense.

In setting Mattis’s deputy Patrick Shanahan to take over as acting secretary of defense on January 1, 2019, Trump cut Mattis’ tenure by a full two months. The retired four-star general previously led the United States Central Command from 2010 to 2013. Trump noted that Shanahan is a former Boeing executive—the Times adds that aides feel Trump likes him “in part because he often tells the president that he is correct to complain about the expense of defense systems.”

Trump, meanwhile, has resumed defending his decision to withdraw U.S. troops from Syria, and offering Twitter sympathy for the tsunami disaster in Indonesia. The government shutdown looms as well, but won’t make progress until December 27 at the earliest, when senators reconvene to discuss Trump’s wall demands. In this White House, plenty of turnover could fill that time.