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 need a dialogue with the Iranians, and it is going to take both carrots and sticks. We employed very tough economic sanctions, and they are having an effect. But we also have to give the Iranians an idea of what the economic and cooperative possibilities would be if they did give up their quest for a nuclear weapon.

Leadership must be established from the top down.

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.

I don't think that within a certain amount of time we can get rid of all nuclear weapons. But I do believe that, step by step, we could get others to join us. I call it going up the mountain. We can get to the top eventually, but we have to get to base camp first. Right now, we are in the valley. So we have a long way to go, but maybe our children or our grandchildren will see the top of the mountain.

Some people think we will see a nuclear explosion in Europe or the United States within the next 10 years. Will it happen? Sure, it's possible. But I think we can greatly diminish that risk. The only way you can do that is through cooperation, and it has to be global.

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