UPDATE: Here is Mattis' resignation letter. In it, he details serious differences with President Trump on global views and approach to foreign policy.
NEW: Mattis's resignation letter, via @Elizabeth_McLau: "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." pic.twitter.com/u2cPrgQQKV— Conor Finnegan (@cjf39) December 20, 2018
Mattis: "My views on treating allies with respect & also being clear-eyed about both malign actors & strategic competitors are strongly held & informed over four decades of immersion in these issues." (This is brutal.)— David M. Drucker (@DavidMDrucker) December 20, 2018
President Trump announced Thursday afternoon Secretary of Defense James Mattis will be leaving his position at the beginning of next year.
General 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. During Jim’s tenure, tremendous progress has been made, especially with respect to the purchase of new fighting....— Donald J. Trump (@realDonaldTrump) December 20, 2018
....equipment. General Mattis was a great help to me in getting allies and other countries to pay their share of military obligations. A new Secretary of Defense will be named shortly. I greatly thank Jim for his service!— Donald J. Trump (@realDonaldTrump) December 20, 2018
The move comes less than 24-hours after President Trump announced U.S. troops will be leaving Syria, a decision Mattis, along with a number of other military leaders, strongly disagrees with.
I am told that CENTCOM, in particular, Gen Joe Votel, the head of US Central Command, feels "punched in the gut" by the decision to withdraw troops from Syria. US military commanders were "shocked" by the President's decision, but now are making plans to withdraw.— Jennifer Griffin (@JenGriffinFNC) December 20, 2018
Trump gave military 30 days to pull out. Pentagon chiefs fear the SDF, who fought with US vs ISIS and Kurdish forces to be slaughtered.— Jennifer Griffin (@JenGriffinFNC) December 20, 2018
As one senior US defense official put it to me, "no one will ever work or fight with us in the Middle East again." https://t.co/9CoGjpAPHR
Meanwhile, President Trump is also working on a troop draw down in Afghanistan.
A senior US official, tells me President Trump planning a “significant drawdown” of US troops in Afghanistan. This source tells me that it would involve MORE THAN 3,000 US troops pulling out. Confirming @glubold @jessdonati WSJ scoop.— Jennifer Griffin (@JenGriffinFNC) December 20, 2018
No word yet on Mattis' replacement.