Who Will Replace Jim Mattis? Trump Says He’ll Name A New Defense Secretary “Shortly”

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President Donald Trump's Defense Secretary Jim Mattis, whom he once fondly referred to as one of "my generals," is leaving. On Thursday, Trump tweeted about Mattis' "retirement," saying a replacement will be forthcoming without mentioning any names.

"Gen. Jim Mattis will be retiring, with distinction, at the end of February, after having served my administration as secretary of defense for the past two years," Trump wrote. Trump also noted that he was grateful for Mattis' time in his administration and would announce his successor "shortly," although he didn't specify when.

Trump largely praised Mattis in his tweets. However, Mattis' letter to the president, released right after Trump tweeted, referred to his departure as a resignation. "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. He also notably did not thank the president in his letter.

Thursday's news of Mattis' departure comes a day after The Washington Post reported, based on interviews with anonymous United States officials, about Trump and Mattis' fractured relationship. One of the main points of contention between both men reportedly involved Trump and Mattis' differing views on America's military presence in Syria.

While the president has announced that American troops will leave Syria, anonymous officials told The Post that Mattis said such a departure would cause turbulence in the Middle Eastern region. Trump's sudden announcement about Syria has been widely criticized.

In his resignation letter, Mattis also wrote, "One core belief I have always held is that our strength as a nation is inextricably linked to the strength of our unique and comprehensive system of alliances and partnerships."

"While the U.S. remains the indispensable nation in the free world," Mattis added, "we cannot protect our interests or serve that role effectively without maintaining strong alliances and showing respect to those allies."

While Mattis did not specify which allies Trump had insulted in the past, he may have been referring to Trump hurling insults at Germany at the NATO annual summit in July. That summer, Trump called Germany a "captive of Russia" and that it was "making Russia richer."

It was at that controversial diplomatic meeting that a terse NATO Secretary General Jens Stoltenberg said, "In the history of NATO we have had many disagreements and we have been able to overcome them again and again."

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In spite of their differences, Mattis wrote in his resignation letter that he would ensure that a transition took place sans trouble.

"I pledge my full effort to a smooth transition that ensures the needs and interests of the 2.15 million Service Members and 732,079 Department of Defense civilians receive undistracted attention of the Department at all times so that they can fulfill their critical, round-the-clock mission to protect the American people," he wrote.

Mattis is now joining the roster of at least a dozen figures that have been either fired or have resigned from Trump's tumultuous cabinet.