What Donald Trump is doing is serving the polluters and serving a narrow group of ideological interests. That's not leadership. That's abdication of responsibility, and this step does not make America first. It makes America last.

George Bush sold us on going to war with Iraq based on the threat of weapons of mass destruction. But we still haven't found them.

I want to start by saying something nice about President Bush. Of all the presidents we've had with the last name of Bush, his economic plan ranks in the top two.

I had a chance to talk with President [Vladimir] Putin and he clearly said to me very directly, "I will think about that. I will think about this challenge of how we win." Look, this is not easy for Putin. Everybody says, "Oh, Putin's made a big move." Well, Putin is [in Syria] now; and if he wants to fight ISIL alone, that's a challenge, folks.

Those who deny the science or choose excuses over action are playing with fire.

I'm going to be a president who believes in science.

President Clinton was often known as the first black president. I wouldn't be upset if I could earn the right to be the second.