President Donald Trump tweeted Sunday morning that Defense Secretary James Mattis will be replaced Jan. 1 by his deputy — nearly two months before his planned departure. 

Mattis issued a resignation letter earlier this week to Trump,  stating that he had grown too disillusioned by his boss’s treatment of other U.S. allies and his “America first” philosophy. He had planned to remain in place through February to give time for an orderly transition, then came this latest presidential tweet. 

Patrick Shanahan, current deputy secretary of Defense, will become acting head of the Pentagon, according to Trump.

I am pleased to announce that our very talented Deputy Secretary of Defense, Patrick Shanahan, will assume the title of Acting Secretary of Defense starting January 1, 2019. Patrick has a long list of accomplishments while serving as Deputy, & previously Boeing. He will be great!

— Donald J. Trump (@realDonaldTrump) December 23, 2018

Mattis was widely considered by lawmakers as Trump’s wisest hire, and was seen as a moderating influence on the unpredictable president.

“Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position,” Mattis wrote in his letter on Dec. 20. 

The retired four-star Marine general was at odds with the president on many issues, including Trump’s abrupt decision to withdraw American troops from the conflict in Syria and reduce troop presence in Afghanistan.  Mattis submitted his resignation after Trump made a video announcement that he was withdrawing U.S. troops in Syria — a decision that was panned by Republicans and Democrats alike. 

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