Why do soldiers fight? They join because they believe in a higher cause -- protecting religion, their nation, defending against a foreign nation. But why do soldier stay and fight? Soldiers aren't individuals. They are part of a unit. And that unit is led by a commander. If they don't trust their commander ... if there is no leadership, there is nothing.

Certainly, we shouldn't go about making a habit of taking generals and making them secretary of defense.

[General James Mattis] a very talented individual. He's - has a personal library of about 10,000 books and he's read most of them on military history and strategy and so forth.

Michele Flournoy, by the way, is not just a talented and bright person. She was Hillary Clinton's secretary of defense in-waiting. So for her to give General [James] Mattis her support, that says something significant.

I think this does show that there will be some changes, not so much in Europe or Asia but certainly in the Middle East. General [James] Mattis has called for a comprehensive strategy to combat the various enemies the United States faces in the Middle East, especially Iran.

General [James] Mattis has said that the deal's in place. We can't unilaterally pull out of it without support from our allies because the sanctions wouldn't bite as deeply. And so he'll find other ways to push back against Iran in the various conflicts that Iran is fomenting around the [Iran] region.

Given this president [Donald Trump] and his lack of military experience, I think it actually might be a good thing to have someone who understands the military very deeply to be counseling him.