'Mad Dog' Mattis sleeps well, keeps others awake
By Associated Press
May 28, 2017 11:46 AM CDT
Secretary of Defense James Mattis walks into Michie Stadium to give the commencement address, Saturday, May 27, 2017, in West Point, N.Y. Nine Hundred and thirty six cadets received their diplomas, most of whom will be commissioned as second lieutenants in the army. (AP Photo/Julie Jacobson)   (Associated Press)

WASHINGTON (AP) — Watch out for the "Mad Dog" when the sun goes down.

That's the message Sunday from Defense Secretary Jim Mattis, whose nickname has been used by President Donald Trump on Twitter.

The Pentagon chief is a battle-hardened, tough-talking retired Marine Corps general who was entrusted with some of the most challenging commands in the military.

So what might you expect him to say when asked, "What keeps you awake at night?"

Maybe another missile launch from North Korea? An attack by Islamic State militants? An incident in the South China Sea?

"Nothing," he tells CBS' "Face the Nation."

"I keep other people awake at night."