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.

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.

Seventeen years after the Cold War, how can it be in the Unites States' national security interest for the President of Russia to have only a few minutes to decide whether to fire his nuclear weapons or lose them in response to what could be a false warning?

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 Iranians know that if they develop nuclear weapons, they will be in tremendous jeopardy from military capabilities of their neighbors and of the United States. I am not predicting what will happen in 2013, but I do think it is a crucial year. I hope we can make it clear to the Iranians that we do not object to them having peaceful use of nuclear power. But when they enrich Uranium to a 20 percent level, people think they are going for the bomb. Their uranium enrichment program is a real danger.

Leadership must be established from the top down.