Jim Mattis has resigned on principle as Pentagon chief after President Trump decided to slash U.S. troop presence in Syria and Afghanistan, citing in a letter the need for "a Secretary of Defense whose views are better aligned" with the president's.

In his strikingly frank resignation letter, Mattis issued what amounted to a stark rebuke of Trump. He outlined his beliefs in alliances, opposition to Russia and China, being respectful to allies, and standing up to authoritarianism before concluding that Trump differed with him on key principles.

He said, "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."

Trump announced Wednesday that all U.S. troops would be withdrawn from Syria. There were reports Thursday that he intended to pull out thousands of troops from Afghanistan. Mattis reportedly told the White House early Thursday he needed to speak with Trump. The two met in the Oval Office at 3 p.m., and Mattis tried — and failed — to persuade Trump to keep American forces in Syria. At that point, Mattis decided to quit.

Minutes before Mattis, 68, released his letter, Trump announced via Twitter that Mattis, a former four-star general in the U.S. Marine Corps, would be retiring "with distinction" at the end of February.

“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," Trump said in a series of tweets Thursday, "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!”



....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



In the resignation letter, Mattis praised Trump administration accomplishments, including "improving the readiness and lethality in our forces," and he told Trump that he would remain at the Pentagon until Feb. 28.

But Mattis also suggested his decision was based on differences with Trump, and he even appeared to directly criticize the president, suggesting he concurred with Trump antagonists who claim Trump has treated allies shabbily.

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

“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,” Mattis wrote. “We must do everything possible to advance an international order that is most conductive to our security, prosperity and values, and we are strengthened in this effort by the solidarity of our alliances.”

The announcement comes a day after Trump claimed that ISIS had been “defeated” and after the Pentagon announced that troops were being withdrawn from Syria. The Pentagon directly contradicted Trump the same day, acknowledging that efforts to eliminate ISIS had not concluded.

Earlier on Thursday, just before Mattis's resignation became public, it was also reported that Trump was considering a massive withdrawal of the approximately 14,000 troops in Afghanistan as well. Some reports suggest this and the Syria decision helped prompt Mattis to quit.

Mattis has frequently dismissed media reports suggesting that his days at the Pentagon would be limited. For example, Mattis indicated to reporters in September that he was not considering leaving his post and instead said, "I think about doing my job each day."

“Of course I don’t think about leaving. I love it here. I’m thinking about retiring right here. I’ll get a little place down on the Potomac,” Mattis said.

Trump and Mattis were once close but have reportedly grown distant in recent months, meeting less frequently than they had earlier in his term.

The two have clashed on several issues. Trump reportedly specifically overruled Mattis with his decision to withdraw troops from Syria.

In an October interview on CBS’ "60 Minutes," Trump labeled Mattis “sort of a Democrat."

