Immigration is the most difficult issue I've ever dealt with, and I've dealt with some tough issues: drones, gays in the military, WikiLeaks, Guantanamo. But immigration is hardest because there are so few people willing to talk and build consensus. Everybody's firmly made up their mind. It's a polarized issue.

Under well-settled legal principles, lethal force against a valid military objective, in an armed conflict, is consistent with the law of war and does not, by definition, constitute an 'assassination.'

In my view, targeted lethal force is at its least controversial when it is on its strongest, most traditional legal foundation. The essential mission of the U.S. military is to capture or kill an enemy. Armies have been doing this for thousands of years. As part of a congressionally authorized armed conflict, the foundation is even stronger.

ISIL, AQ, now have the ability to literally reach into our homeland through social media, through the Internet, to recruit and inspire. It makes for a more complicated homeland security environment. And so it requires a whole of government approach, not just military and law enforcement, homeland security, aviation security, and the like.

Democratic leaders, whose power is ultimately dependent on popular support, are held accountable for failing to improve the lives of their citizens. Therefore, they have a powerful incentive to keep their societies peaceful and prosperous.

Good leaders need a positive agenda, not just an agenda of dealing with crisis.

I think we so often equate leadership with being experts - the leader is supposed to come in and fix things. But in this interconnected world we live in now, it's almost impossible for just one person to do that.

President Obama, like every other leader on Earth, is still going to be looking out for national and economic interests. States don't cease to be states overnight just because they get a great visionary as their new president.