U.S. Defense Secretary Jim Mattis is resigning, saying his views were not fully "aligned" with President Donald Trump and citing policies toward Russia and China as among the differences.
The December 20 announcement of Mattis' departure came one day after Trump announced that he was withdrawing U.S. forces from Syria, a decision that came over the objections of Mattis and other senior advisers.
In a letter released shortly after Trump announced on Twitter that Mattis was leaving in February 2019, the Pentagon chief made clear his disagreements with Trump.
"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," Mattis wrote.
U.S. lawmakers, both Democratic and Republican, immediately expressed alarm over the departure of Mattis, who is seen by many as a steadying hand in the administration.
Senate Democratic leader Chuck Schumer told reporters the resignation was an indication of "chaos" in the U.S. administration, while Nancy Pelosi, soon to be the House speaker, said she was "shaken" by Mattis' resignation letter.
"You have great leaders who have left this administration in dismay," she said at an impromptu press briefing. "Others have left in disgrace."
Democrat Mark Warner, the Senate Intelligence Committee vice chairman, wrote on Twitter that "this is scary" and that "Mattis has been an island of stability amidst the chaos of the Trump administration."
The top Republican in the Senate, Mitch McConnell, said it was "regrettable" that Mattis was leaving the administration, and rebuked Trump.
He added that the United States must "maintain a clear-eyed understanding of our friends and foes, and recognize that nations like Russia are among the latter."
Republican Senator Marco Rubio wrote on Twitter: "Just read Gen. Mattis resignation letter. It makes it abundantly clear that we are headed toward a series of grave policy errors which will endanger our nation, damage our alliances & empower our adversaries."
In his letter, Mattis did not mention his disagreement over Trump's Syria decision, nor proposed deep cuts to U.S. forces in Afghanistan.
'Difference Of Opinions'
Trump surprised many advisers, as well as allies, with his announcement on December 19 that he was ordering the withdrawal of approximately 2,000 U.S. troops from Syria. Those troops have been working closely with Kurdish forces, helping to root out Islamic State (IS) militants.
Republican Senator Lindsey Graham, a close ally of Trump, criticized the withdrawal decision, and said Mattis had told him that when the U.S. forces leave "it's going to be open season on every Kurd who's supported us."
Mattis' departure is the latest in a flurry of announced exits from the U.S. administration as Trump nears the halfway point in his four-year term.
U.S. President Donald Trump (right) with Defense Secretary Jim Mattis in 2017
It comes a day after Trump surprised and angered many U.S. military leaders, lawmakers, and international allies by announcing he was withdrawing "all" U.S. troops from Syria, where they are assisting a Syrian Arab and Kurdish alliance fighting against IS militants and other forces.
News agencies are reporting that Mattis and other national-security aides opposed the decision, saying it handed Russia, Iran, and Turkey a victory. Reuters quoted an unnamed senior White House official as saying that Mattis resigned during a meeting with Trump after the two had a difference of opinions "on some issues."
Reports also surfaced late on December 20 that Trump was planning to withdraw a "significant" number of U.S. forces from Afghanistan.
Split With Trump
The 68-year-old Mattis, a Marine Corps general, was one of the most respected members of the Trump administration and had won praise from both Democrats and Republicans. Some, however, have criticized Mattis for not standing up to Trump for policies that many in Congress have opposed.
In his resignation letter, Mattis said, "I believe we must be resolute and unambiguous in our approach to those countries whose strategic interests are increasingly in tension with ours.
"It is clear that China and Russia, for example, want to shape a world consistent with their authoritarian model gaining veto authority over other nations' economic, diplomatic, and security decisions to promote their own interests at the expense of their neighbors, America, and our allies."
Mattis added that his views of "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."
"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 said.
Minutes earlier, Trump wrote on Twitter that "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...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!" Trump added.
Latest Departure
Trump has often been criticized by Democrats and even many Republicans for policies that they assert are too soft on Russia and too antagonistic toward traditional allies, such as fellow NATO members.
Asked for a reaction to Mattis' departure, NATO spokeswoman Oana Lungescu told RFE/RL, "Secretary Mattis has made a key contribution to keeping NATO strong and ready to deal with the significant security challenges we face, while ensuring a fairer share of the burden across our alliance."
Lungescu added that NATO chief Jens Stoltenberg "will continue to work closely with Secretary Mattis until the end of his term, as he expects to work closely with his successor."
"We are grateful for the iron-clad commitment of the United States to NATO. US leadership keeps our transatlantic alliance strong."
Trump announced on December 8 that John Kelly, a retired Marine Corps general, would be leaving his post as White House chief of staff by the end of the year.
Trump and Kelly had been rumored to be at odds over many issues, with some U.S. media reporting the two are no longer speaking to each other.
Among other recent departures, Jeff Sessions, Trump's attorney general, was forced out of his position on November 7, while U.S. Ambassador to the UN Nikki Haley said on October 9 that she would step down at the end of the year.
Secretary of State Rex Tillerson was fired on March 13 after disagreements with the president. Trump later tweeted that Tillerson was "dumb as a rock" and "lazy as hell" after Tillerson said Trump was "pretty undisciplined," and did not read.