Senate Majority Leader Mitch McConnell urged President Trump late Thursday to pick a defense secretary who shares Jim Mattis' views, particular of which nations are U.S. allies and which are enemies.

"We must also maintain a clear-eyed understanding of our friends and foes, and recognize that nations like Russia are among the latter. So was sorry to learn that Secretary Mattis, who shares those clear principles, will soon depart the administration," McConnell said in a statement. "But I am particularly distressed that he is resigning due to sharp differences with the president on these and other key aspects of America’s global leadership."

Trump announced Thursday evening the four-star Marine Corps general would be retiring in February.

Minutes later, Mattis said he was resigning over the need for a Defense secretary "whose views are better aligned" with Trump's.

“It is regrettable that the president must now choose a new Secretary of Defense. But I urge him to select a leader who shares Secretary Mattis’s understanding of these vital principles and his total commitment to America’s servicemembers," McConnell said.

The parting of ways comes a day after Trump said he was withdrawing all U.S. troops in Syria and on the same day reports emerged that he intended to draw down troops in Afghanistan.

White House press secretary Sarah Sanders told reporters Thursday night that Trump and Mattis have a "good relationship," despite Mattis's departure, which included a statement pointing to policy differences and suggesting Trump had harmed relationships with allies.

"They had a long conversation, but again, they have a good relationship and we expect them to continue to have a good relationship. The president has a great deal of respect for Secretary Mattis and he is going to stay on for another couple of months, I think that is a great indicator of the type of cooperation they have," Sanders said at the White House.