If in order to kill the enemy you have to kill an innocent, don't take the shot. Don't create more enemies than you take out by some immoral act.

Nothing keeps me awake at night. I keep other people awake at night.

I'm from the American West. We have forest fires out there. And some of the worst forest fires in our history, the most damage were caused when we pulled the fire crews off the line too early. And so we're going to have to continue to keep the pressure on the enemy - ISIS. There's no room for complacency on this.

A country that armed Stalin to defeat Hitler can certainly work alongside enemies of al-Qaida to defeat al-Qaida.

Our world is becoming darker. The dangers are increasing from North Korea, whose recent provocation underscored the need to impose a higher price on this rogue regime, a problem that is not just the United States alone, but a problem for us all.

Since 9/11 we've been engaged in wars around the world, and General [James] Mattis has been a leading battlefield commander in many of those theaters, including in the April 2004 siege of Fallujah, where the US Marines killed so many people that the municipal soccer stadium in the city had to be turned into a graveyard for the dead.

I would consider the principal threats to start with Russia, and it would certainly include any nations that are looking to intimidate nations around their periphery, regional nations nearby them, whether it be with weapons of mass destruction or, I would call it, unusual, unorthodox means of intimidating them, that sort of thing.