After a regime is removed, however, it is dangerous to leave a security vacuum.

The American people are pretty impressive in their ability to keep after something if they think it is doable.

That sense of what happened in Europe in World War II has shaped a lot of my views.

I certainly think it's important to speak up and say how unacceptable Donald Trump is. I'm always more than willing to do that.

Our security depends on having good relationships with our allies. Donald Trump mainly shows contempt for them.

The most striking thing is that even before Osama bin Laden was killed, he seemed largely irrelevant to the Arab Spring.

Islamic State is mainly a direct result of the failure in Syria. That's where IS has grown. That's where IS spread from.