Debating, doubting, or rejecting the basic scientific facts about climate change in the face of the overwhelming evidence and overwhelming scientific opinion will not change those facts.

When Hillary Clinton ran against Senator [Barack] Obama she thought him naive because he thought it was a good idea to talk to our enemies. I think those are exactly the people you have to talk to and you have to negotiate with.

What I do know is that drones are a modern weapon. When used effectively, when taking out ISIS or terrorist leaders, that's pretty impressive. When bombing wedding parties of innocent people and killing dozens of them, that is, needless to say, not effective and enormously counterproductive. So whatever the mechanism, whoever is in control of that policy, it has to be refined so that we are killing the people we want to kill and not innocent collateral damage.

We have to transform our energy system.

The basic issue of an American society which is fair, which is providing opportunity for all, is nowadays being replaced by the correct perception that we're living in a rigged economy - where it doesn't matter how hard you worked, the result will be all the income goes to the people at the very top. It's leading to a lot of frustration and anger, and people want some fundamental changes to the way we do economics and growth.

If you are not prepared top take care of the men and women who put their lives on the line to defend this country - who came back wounded in body, wounded in spirit - if you're not prepared to help those people, then don't send them to war in the first place.

I think my main concern is because I worry about demagoguery. It`s real. You see the people standing up there and applauding.