"President Trump is plunging the country into chaos," Senate Minority Leader Chuck Schumer said on Thursday. "The market's down another 500 points, General Mattis is stepping down and we know he has real disagreements with the president in Syria and on the wall."
Republican Senator Marco Rubio said Mattis' resignation makes it clear that the United States is headed towards a series of grave policy errors that will endanger the country, damage its alliances and empower its adversaries.
Senator Dick Durbin said the United States has lost the "adult in the room when the President goes off on a tweet-filled, uninformed rant about our national security."
Senator Lindsey Graham said via Twitter that Mattis is a man of intellect and integrity, who had been in the fight against radical Islam for decades and provided sound and ethical military advice to Trump.
Speaker of the House of Representatives Paul Ryan said the United States has become a safer country at home and a more commanding force overseas with Mattis serving as the head of the Department of Defense.
On Thursday, Mattis in a resignation letter said he was stepping down at the end of February citing the fact that Trump needed to find a defense chief whose views were more aligned with his own. The move came a day after the White House said the United States was withdrawing troops from Syria.
The United States cannot protect its interests without maintaining strong alliances and showing respect to allies, Mattis said.
Moreover, Mattis said the United States must utilize all tools in its power to provide for the common defense against Russia and China, which want to shape a world consistent with their authoritarian model to promote their own interests at the expense of their neighbors. The United States must be resolute and unambiguous in its approach to countries whose strategic interests are increasingly in tension with the United States.
Mattis recommended that a full transition to a new Secretary of Defense occur well in advance of the transition of the new Chairman of the Joint Chiefs of Staff in September in order to ensure stability in Defense Department. Mattis will be retiring at the end of February. The announcement came shortly after Trump's decision to pull out all US troops from Syria.
Daesh (also known as ISIS/ISIL/IS) is a terrorist group banned in Russia.