Defense Secretary Gen. James Mattis weighed in on several national security issues in his interview with CBS’ John Dickerson, which aired Sunday on Face the Nation. The experienced general shared his opinion on NATO and the Paris climate agreement, while offering sneak peeks of how the U.S. plans to respond to Russian threats, the rise of ISIS, and North Korea’s ballistic missile tests.

The U.S. will not tolerate these aggressions from North Korea, he said, noting that war with the regime would be “catastrophic.”

Yet, this exchange halfway through Mattis and Dickerson's conversation stood out in epic form.

JOHN DICKERSON: What keeps you awake at night? SECRETARY JAMES MATTIS: Nothing. I keep other people awake at night.

This is what you hope for in a defense secretary – someone who is not going to show any signs of weakness to the enemy.

They don't call him "mad dog" for nothing.