Do I believe Edward Snowden contributed to the rise of ISIS? Yes. Would they have gotten there without the help he provided them? Probably. Would they have been able to conduct this attack in Paris without him? Maybe. So the honest answer is I don't know.

You have to have a military and intelligence approach to removing leadership that results in rapid frequent removals from the battlefield. It's got to be one, two a week, not just one or two every three or four months.

One great lesson from history we need to keep on re-learning. It is that sometimes your adversaries tell you exactly what they're going to do. How many times did [Osama] bin Laden say prior to 9/11 that he was coming after the U.S.? ISIS made clear that when they established their caliphate in Iraq and Syria, they were coming after the United States too.

From Mr. [Donald] Trump's perspective, right, he simply heard [Vladimir] Putin compliment him. He then responded by complimenting him. He never thought that he might be being played.

The [Edward] Snowden disclosures created this perception that people's privacy was being put at significant risk.

I'm concerned, too, about ISIS' ability, right, to infiltrate people. But we have got some very effective, robust processes for vetting people. We brought in thousands of Iraqi refugees after the Iraq War. Not a single one has ever turned out to be a terrorist because the vetting was so good.

The thing we've learned from the last 20 years of counterterrorism is the significant value you get from removing leadership from the battlefield in degrading the organization.