What I know concerns me. What I don't know concerns me even more. What people aren't telling me worries me the most.

I think that Vladimir Putin is certainly getting a lot of publicity for what the Russians are doing. And I'm not sure that's unwelcome to him. I think this is a guy who saw the U.S. basically come out against him in his reelection campaign in 2012. He saw the U.S. being behind all of the color revolutions in Eastern Europe and in Georgia and Ukraine and so on. So his view is the West has been interfering in his politics for years.

What I know concerns me. What I don't know concerns me even more. What people aren't telling me worries me the most.

We should never lose sight of the ethos that has made the Marine Corps - where 'every Marine is a rifleman' - one of America's cherished institutions and one of the world's most feared and respected fighting forces

When I was the director of Central Intelligence in the early '90s, I tried to get the Air Force to partner with us in building drones. And they didn't want to, because they had no pilots.

If possible, to be in a position to announce who is going to step in as the interim immediately. And if possible, to announce who you're going to nominate to replace that person. For that to be somebody of impeccable integrity and reputation disarms a lot of the worst criticism that it's some kind of a power play. It's a professional approach to replacing a senior official, which is always going to get a lot of attention.

I don't know General Michael Flynn well, but it's hard for me to believe anybody would allow themselves to be blackmailed by the Russians because they didn't tell the full story or didn't tell the truth to the vice president of the United States who works 50 feet down the hall.