After Defense Secretary James Mattis offered a very public rebuke of President Trump’s characterization of his departure from the administration by way of making his resignation letter public, Trump has decided to push the former Marine General out of his position two months sooner than expected. Patrick Shanahan, who has served as the Deputy Secretary of Defense under Mattis since July of last year, will take on the role of Acting Defense Secretary at that time.

“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!” Trump tweeted on Sunday.

James Mattis, widely seen as perhaps the most well-respected member of Trump’s cabinet by lawmakers on either side of the aisle, resigned rather publicly late last week, citing a laundry list of things he and the president failed to see eye-to-eye on and seemingly making an argument in favor of the diplomatic norms that characterized American foreign policy for decades leading up to Trump taking office.

Mattis, of course, isn’t without his critics, with many conservatives seeing his approach to conflicts in Syria and Afghanistan as “hawkish,” or perhaps too in keeping with a status quo that has allowed the war on terror to become something of a “forever war” over the better part of the past two decades. Trump has already announced plans to withdraw troops from both conflicts.

Critics of Trump’s planned withdrawal call it a political stunt bereft of military strategy, and point to the resignations of Mattis and Brett McGurk, the special presidential envoy for the global coalition to counter ISIS, as signs of the President’s poor understanding of defense strategy and foreign policy as a whole.

Mattis’ resignation pointed to remaining in office until February 1, allowing enough time to find and vet a replacement amid active searches for a chief of staff and other important roles within the administration. However, after Mattis’ strongly worded resignation hit the media, it seems Trump is eager to see the former general out of the Pentagon.

“My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues,” wrote Secretary Mattis.

With Shanahan as acting Defense Secretary, Trump faces an uphill battle to find a permanent replacement

Read Next: With Shanahan as acting Defense Secretary, Trump faces an uphill battle to find a permanent replacement

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

Shanahan was approved to serve as Deputy Defense Secretary last July by an overwhelming margin, despite some clashes with the late Senator John McCain.