An aggressor nation or extremist group could gain control of critical switches and derail passenger trains, or trains loaded with lethal chemicals.

My impression is that Putin feels that he can basically manipulate the West to do what he ultimately wants to achieve, and that he feels he's gotten away with it so far, and that all he has to do is basically play the same game.

The political and substantive reality is that the agenda has to change. I don't think they have any choice.

Caution is an important quality in a leader, but it has to be caution followed by decision. Caution followed by ambivalence can be a weakness.

If you're a terrorist, you're a terrorist.

Al Qaeda still remains a threat.

I have tremendous confidence in the ability of government institutions and the American people to do what is right to make sure that our democracy stays on the right track.