CHUCK TODD: I’ll put up some headlines from some of them. You’ve seen them. “It’s time for these officials to come to the aid of their country." Trump is in freefall. We need insights on his fitness from Mattis, Kelly, and others. Now." "Those who work with Trump must now tell Congress what they know.” First of all, if Congress subpoenaed you, and -- for to try to find out what you knew about decision-making processes, when it came to Ukraine or other things, would you cooperate?

MATTIS: Well, I’d have to know, specifically, what it was about. I mean, I obey the law. ... So that’s not the issue. But again, remember that the Defense Department stays outside of politics for a reason. There’s a longstanding tradition, why you do not want the military to be engaged in politics. ...

TODD: You feel like it’s pretty -- do you feel like your resignation letter is pretty clear, what you think? Like, what more do you need to add, as you’re saying.

MATTIS: It’s a page and a half long. It talks about our, our security being tied, inextricably, to our alliances. I don’t know what more I could say about how I think we ought to treat allies and how we should treat those who are adversaries.