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

You can overcome wrong technology. Your people have the initiative, they see the problem, no big deal ... you can't overcome bad culture. You've gotta change whoever is in charge.

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.

Fight with a happy heart and strong spirit.

The American people and the American military will never get used to civilian casualties. And we will - we will fight against that every way we can possibly bring our intelligence and our tactics to bear. We're not the perfect guys, but we are the good guys.

You cannot allow any of your people to avoid the brutal facts. If they start living in a dream world, it's going to be bad.

The importance of strengthening Euro-Atlantic security: the growing dangers pile pressure on our rules-based international system, so we need to do more to strengthen NATO, the bedrock of our defense - not just upping spending, but making the alliance more agile and more capable of tackling dangers from all directions.