Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE announced Thursday he would resign at the end of February, sending a note to President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE saying he deserved a secretary "whose views are better aligned with yours."



The announcement came a day after the White House said the U.S. would be withdrawing its troops from Syria, as well as reports it was also considering a drawdown in Afghanistan. Both moves have been met with opposition by Pentagon officials and members of the foreign policy establishment.



In a striking resignation letter to Trump notable as much for what it did not say as what was included, Mattis signaled his concern with the way Trump treated allies in NATO as well as rivals such as China and Russia.

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He wrote that his

“core belief” is that U.S. strength is “inextricably linked with the strength of our unique and comprehensive system of alliances and partnerships.”“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 conducive to our security, prosperity and values, and we are strengthened in this effort by the solidarity of our alliances.”

"Because you have a 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.

The letter did not mention Trump and did not include statements typically found in resignation letters about it having been an honor to serve the president. It was addressed "Dear Mr. President," and concluded with a line about how it had been an honor to serve the nation and "our men and women in uniform."

A former White House official who worked closely with Mattis' team described the letter as “a 21 gun f--- you.”

Congressional reaction to the Mattis resignation was gloomy, with House Democratic Leader Nancy Pelosi Nancy PelosiHoyer: House should vote on COVID-19 aid — with or without a bipartisan deal Ruth Bader Ginsburg lies in repose at Supreme Court McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE (D-Calif.), the likely next Speaker of the House, saying it had left her shaken.

"I am shaken by the resignation of Gen. Mattis and pray for our country," Pelosi told reporters at a press conference held over the looming government shutdown — the backdrop for the defense chief's news.

"This is a sad day for America because Secretary Mattis was giving advice the President needs to hear," Sen. Ben Sasse Benjamin (Ben) Eric SasseTrump says he'll sign order aimed at protecting premature babies in appeal to religious voters Government watchdog recommends creation of White House cyber director position Chamber of Commerce endorses McSally for reelection MORE (R-Neb.) said in a statement.

"Mattis rightly believes that Russia and China are clear adversaries and that we are at war with jihadists across the globe who plot to kill Americans at home. Isolationism is a weak strategy that will harm Americans and America’s allies. Radical Islamic jihadists are still at war with us, and no ISIS is not gone."

Mattis specifically highlighted NATO and the coalition fighting the Islamic State in Iraq and Syria (ISIS) as example of alliances for which America must provide “effective leadership.”

Trump has frequently derided NATO as outdated and chastised allies to pay more for their own defense. At a NATO summit in July, Trump reportedly threatened to withdraw the United States from the alliance if allies did not increase their defense spending.



Trump’s Wednesday announcement that he will withdraw from Syria, meanwhile, rattled allies in the anti-ISIS coalition who were not informed beforehand. It was also widely criticized as abandoning the U.S.-backed forces fighting ISIS on the ground in Syria, including Kurdish forces threatened with attack by Turkey.



Several lawmakers have said Mattis made clear to them he did not agree with Trump’s decision.

Sen. Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.) earlier Thursday said that Mattis “thought that the time was not right to leave” Syria and was “very worried about the Kurds."

Mattis’s letter was released minutes after Trump said on Twitter that the secretary was "retiring."



"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," Trump tweeted.

Trump also praised Mattis for his efforts to boost the defense budget and work to increase allies’ defense spending.



“During Jim’s tenure, tremendous progress has been made, especially with respect to the purchase of new fighting equipment,” Trump tweeted. “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!”

Mattis offered his resignation to Trump on Thursday during a meeting at the White House that included a “long conversation” touching on their policy differences, according to White House press secretary Sarah Huckabee Sanders.

Sanders, however, downplayed the level of tension between Mattis and Trump, saying “they agree to disagree at times, but that doesn’t mean you can’t have a good relationship with somebody.” She also said Trump believes hearing different viewpoints is a “good thing.”

“The president always listens to the members of his national security team, but at the end of the day, it’s the president’s decision to make,” she said.

Trump plans to name a replacement for Mattis by year's end, according to Sanders, who did not name any candidates under consideration.

Rumors of Mattis’s potential departure have swirled for months as Trump bucked his defense secretary’s advice on a number of issues.



Over the last couple of years, Trump announced a ban on transgender troops on Twitter, canceled joint U.S.-South Korea military exercises, withdrew from the Iran nuclear deal and deployed troops to the U.S.-Mexico border, among other moves that Mattis either opposed or received little forewarning of.



Recently, Trump passed over Mattis’s choice of successor for Joint Chiefs of Staff Chairman Gen. Joseph Dunford in favor of Army Chief of Staff Gen. Mark Milley,



But there were also signs Mattis continued to have clout, such as convincing Trump to boost next year’s defense budget to $750 billion.



Reports about growing animosity between the two and Mattis’s possible exit picked up steam in September following the publication of a book from journalist Bob Woodward. In the book, Mattis is quoted as saying Trump’s understanding of the situation on the Korean peninsula is like that of a “fifth or sixth grade.”



At the time, Mattis dismissed rumors of his exit, saying "I wouldn't take it seriously at all” and that people should "keep a sense of humor about it."



Mattis also called Woodward’s reporting “fiction,” and Trump praised that denial.



Mattis set his resignation date as Feb. 28 to allow for “sufficient time” to nominate and confirm a successor, ensure the Pentagon is “properly” represented at upcoming congressional hearings and a NATO defense ministerial, and have the transition happen well before Dunford’s departure in September.

Former GOP Sens. Kelly Ayotte Kelly Ann AyotteBottom line Bottom line Bottom Line MORE (N.H.) and Jim Talent (Mo.) have been mentioned as possible replacements by sources close to the administration.



Mattis has been one of the few Trump Cabinet member to receive bipartisan praise throughout his tenure. Dating back to his nomination, lawmakers saw him as a potentially steadying hand to a volatile president.



In a sign of their faith in him, lawmakers passed a waiver that allowed the retired general to serve as Defense secretary in spite of a law saying the secretary must be out of uniform for at least seven years. At the time, Mattis had only been out of uniform for three years.



On Thursday, Democrats said they saw Mattis’ resignation as a sign of chaos.



“A secretary of Defense quitting over a public disagreement with a president whose foreign policy he believes has gone off the rails is a national security crisis,” Sen. Chris Murphy Christopher (Chris) Scott MurphyDemocratic senator calls for 'more flexible' medical supply chain to counter pandemics The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon GOP chairman to release interim report on Biden probe 'in about a week' MORE (D-Conn.) tweeted. “No way around it.”



Rep. Adam Smith David (Adam) Adam SmithWhen 'Buy American' and common sense collide Overnight Defense: Marine Corps brushes off criticism of Marines' appearance in GOP convention video | US troops injured in collision with Russian vehicle in Syria | Dems ask for probe of Vindman retaliation allegations Democrats press Pentagon watchdog to probe allegations of retaliation against Vindman brothers MORE (D-Wash.), who is expected to be House Armed Services Committee chairman in January, similarly said the resignation “shows that President Trump is now very much out of control.”



“I respect the decision; I understand why he did it. But it's unfortunate for the country,” Smith said.



Smith added that it's "very important" that Mattis be replaced with a figure of his experience and gravitas, but added that he has "no confidence whatsoever that that will be the case."



"It now seems that President Trump is picking people who are simply going to do his bidding."

Jordan Fabian and Mike Lillis contributed