If you think you're a leader, and you look over your shoulder and there ain't nobody following you, man, you're just takin' a walk.

The steady progress made by North Korea on its nuclear and missile programs is deeply concerning. The US cannot solve this problem alone. However, in order to take steps that could fundamentally affect the North Korean leadership and its decision-making, we need to work even more closely with our allies in the region who feel this threat acutely. I would urge China, in particular, to intensify its leadership role in helping to solve this crisis.

You have to pay the price. You will find that everything in life exacts a price, and you will have to decide whether the price is worth the prize.

I think if terrorists had nuclear materials and found people to put a bomb together - both of which are possible - we would already have seen a nuclear explosion. But we have literally thousands of people around the world working their tails off and making a lot of sacrifices to contain nuclear materials. I particularly would like to compliment the Russians on this. In times of great economic distress, many of them could have made an awful lot of money if they had sold their expertise.

If you think you're a leader, and you look over your shoulder and there ain't nobody following you, man, you're just takin' a walk.

We are in a race between cooperation and catastrophe, and the threat is outrunning our response.

There is a pervasive mistrust that grew out of the Cold War and still continues today - even though there are a lot more mutual interests between Europe, Russia and the United States than ever before. But the way we organize things today, it takes years to negotiate. By the time you get a result, the technology has far outrun the policy. So we have to start a dynamic, sustainable type of policy deliberations that can catch up with technology.