james mattis

Jim Mattis, who resigned as Trump's defense secretary nearly a year and a half ago, accuses the president of dividing the nation and warns against "militarizing our response" to protests.

Monday is the Defense Secretary's last day on the job. He urged people to "to support and defend the Constitution while protecting our way of life."

"Because you have the right to have a Secretary of Defense whose views are better aligned with yours ... I believe it is right for me to step down from my position," Mattis wrote to the president.

Former Vice President Joe Biden, actor Warren Beatty, two legendary Arizona athletes and a Russian dissident are among several pallbearers at ceremonies honoring the late senator this week.

In the first update of the National Defense Strategy since 2014, the Pentagon is putting more focus on Russia and China, the "primary concern in U.S. national security," as opposed to terrorism.

Appearing before the Senate Foreign Relations Committee, senior Trump national security officials argued existing use-of-force measures are doing the job, despite being on the books for 16 years.

The president-elect also formally introduced retired Marine Corps Gen. James Mattis as his pick to lead the Defense Department. Congress is also moving to fast-track a waiver he needs to be confirmed.