If you are elected president, what will you take to that office thinking is the single most serious threat to the national security to the United States?
 

KERRY: Nuclear proliferation. Nuclear proliferation. There's some 600-plus tons of unsecured material still in the former Soviet Union and Russia. At the rate that the president is currently securing it, it'll take 13 years to get it.

I did a lot of work on this. I wrote a book about it several years ago -- six, seven years ago -- called "The New War," which saw the difficulties of this international criminal network. And back then, we intercepted a suitcase in a Middle Eastern country with nuclear materials in it. And the black market sale price was about $250 million.

Now, there are terrorists trying to get their hands on that stuff today. 

And this president, I regret to say, has secured less nuclear material in the last two years since 9/11 than we did in the two years preceding 9/11. 

We have to do this job. And to do the job, you can't cut the money for it. The president actually cut the money for it. You have to put the money into it and the funding and the leadership. 

And part of that leadership is sending the right message to places like North Korea.

Right now the president is spending hundreds of millions of dollars to research bunker-busting nuclear weapons. The United States is pursuing a new set of nuclear weapons. It doesn't make sense.

You talk about mixed messages. We're telling other people, "You can't have nuclear weapons," but we're pursuing a new nuclear weapon that we might even contemplate using. 

Not this president. I'm going to shut that program down, and we're going to make it clear to the world we're serious about containing nuclear proliferation. 

And we're going to get the job of containing all of that nuclear material in Russia done in four years. And we're going to build the strongest international network to prevent nuclear proliferation. 

This is the scale of what President Kennedy set out to do with the nuclear test ban treaty. It's our generation's equivalent. And I intend to get it done.
 

LEHRER: Ninety seconds, Mr. President.
 

BUSH: Actually, we've increased funding for dealing with nuclear proliferation about 35 percent since I've been the president. Secondly, we've set up what's called the -- well, first of all, I agree with my opponent that the biggest threat facing this country is weapons of mass destruction in the hands of a terrorist network. And that's why proliferation is one of the centerpieces of a multi-prong strategy to make the country safer. 

My administration started what's called the Proliferation Security Initiative. Over 60 nations involved with disrupting the trans-shipment of information and/or weapons of mass destruction materials. 

And we've been effective. We busted the A.Q. Khan network. This was a proliferator out of Pakistan that was selling secrets to places like North Korea and Libya. We convinced Libya to disarm. It's a central part of dealing with weapons of mass destruction and proliferation.

I'll tell you another way to help protect America in the long run is to continue with missile defenses. And we've got a robust research and development program that has been ongoing during my administration. We'll be implementing a missile-defense system relatively quickly. 

And that is another way to help deal with the threats that we face in the 21st century.

My opponent opposed the missile defenses. 
 

LEHRER: Just for this one-minute discussion here, just for whatever seconds it takes: So it's correct to say, that if somebody is listening to this, that both of you agree, if you're reelected, Mr. President, and if you are elected, the single most serious threat you believe, both of you believe, is nuclear proliferation?
 

BUSH: In the hands of a terrorist enemy.
 

KERRY: Weapons of mass destruction, nuclear proliferation. 

But again, the test or the difference between us, the president has had four years to try to do something about it, and North Korea has got more weapons; Iran is moving toward weapons. And at his pace, it will take 13 years to secure those weapons in Russia. 

I'm going to do it in four years, and I'm going to immediately set out to have bilateral talks with North Korea.
 

LEHRER: Your response to that?
 

BUSH: Again, I can't tell you how big a mistake I think that is, to have bilateral talks with North Korea. It's precisely what Kim Jong Il wants. It will cause the six-party talks to evaporate. It will mean that China no longer is involved in convincing, along with us, for Kim Jong Il to get rid of his weapons. It's a big mistake to do that. 

We must have China's leverage on Kim Jong Il, besides ourselves. 

And if you enter bilateral talks, they'll be happy to walk away from the table. I don't think that'll work.