(L to R) President-elect Donald Trump shakes hands with retired United States Marine Corps general James Mattis after their meeting at Trump International Golf Club, Nov. 19, 2016 in Bedminster Township, N.J. (Photo by Drew Angerer/Getty)
Rachel Maddow

Why Trump's Pentagon pick may prove to be...

Civilian control of the military is a bedrock principle of the American system, which makes retired Marine Gen. James Mattis' nomination problematic.