QUESTION: Yes. Senator McCain, how will all the recent economic stress affect our nation's ability to act as a peacemaker in the world?

MCCAIN: Well, I thank you for that question, because there's no doubt that history shows us that nations that are strong militarily over time have to have a strong economy, as well. And that is one of the challenges that America faces.

But having said that, America -- and we'll hear a lot of criticism. I've heard a lot of criticism about America, and our national security policy, and all that, and much of that criticism is justified.

But the fact is, America is the greatest force for good in the history of the world. My friends, we have gone to all four corners of the Earth and shed American blood in defense, usually, of somebody else's freedom and our own.

MCCAIN: So we are peacemakers and we're peacekeepers. But the challenge is to know when the United States of American can beneficially effect the outcome of a crisis, when to go in and when not, when American military power is worth the expenditure of our most precious treasure.

And that question can only be answered by someone with the knowledge and experience and the judgment, the judgment to know when our national security is not only at risk, but where the United States of America can make a difference in preventing genocide, in preventing the spread of terrorism, in doing the things that the United States has done, not always well, but we've done because we're a nation of good.

And I am convinced that my record, going back to my opposition from sending the Marines to Lebanon, to supporting our efforts in Kosovo and Bosnia and the first Gulf War, and my judgment, I think, is something that I'm -- a record that I'm willing to stand on.

Senator Obama was wrong about Iraq and the surge. He was wrong about Russia when they committed aggression against Georgia. And in his short career, he does not understand our national security challenges.

We don't have time for on-the-job training, my friends.

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BROKAW: Senator Obama, the economic constraints on the U.S. military action around the world.

OBAMA: Well, you know, Senator McCain, in the last debate and today, again, suggested that I don't understand. It's true. There are some things I don't understand.

I don't understand how we ended up invading a country that had nothing to do with 9/11, while Osama Bin Laden and Al Qaeda are setting up base camps and safe havens to train terrorists to attack us.

That was Senator McCain's judgment and it was the wrong judgment.

When Senator McCain was cheerleading the president to go into Iraq, he suggested it was going to be quick and easy, we'd be greeted as liberators.

That was the wrong judgment, and it's been costly to us. So one of the difficulties with Iraq is that it has put an enormous strain, first of all, on our troops, obviously, and they have performed heroically and honorably and we owe them an extraordinary debt of gratitude.

But it's also put an enormous strain on our budget. We've spent, so far, close to $700 billion and if we continue on the path that we're on, as Senator McCain is suggesting, it's going to go well over $1 trillion.

We're spending $10 billion a month in Iraq at a time when the Iraqis have a $79 billion surplus, $79 billion.

And we need that $10 billion a month here in the United States to put people back to work, to do all these wonderful things that Senator McCain suggested we should be doing, but has not yet explained how he would pay for.

Now, Senator McCain and I do agree, this is the greatest nation on earth. We are a force of good in the world. But there has never been a nation in the history of the world that saw its economy decline and maintained its military superiority.

And the strains that have been placed on our alliances around the world and the respect that's been diminished over the last eight years has constrained us being able to act on something like the genocide in Darfur, because we don't have the resources or the allies to do everything that we should be doing.

That's going to change when I'm president, but we can't change it unless we fundamentally change Senator McCain's and George Bush's foreign policy. It has not worked for America.

BROKAW: Senator Obama, let me ask you if -- let's see if we can establish tonight the Obama doctrine and the McCain doctrine for the use of United States combat forces in situations where there's a humanitarian crisis, but it does not affect our national security.

Take the Congo, where 4.5 million people have died since 1998, or take Rwanda in the earlier dreadful days, or Somalia.

What is the Obama doctrine for use of force that the United States would send when we don't have national security issues at stake?

OBAMA: Well, we may not always have national security issues at stake, but we have moral issues at stake.

If we could have intervened effectively in the Holocaust, who among us would say that we had a moral obligation not to go in?

If we could've stopped Rwanda, surely, if we had the ability, that would be something that we would have to strongly consider and act.

So when genocide is happening, when ethnic cleansing is happening somewhere around the world and we stand idly by, that diminishes us.

OBAMA: And so I do believe that we have to consider it as part of our interests, our national interests, in intervening where possible.

But understand that there's a lot of cruelty around the world. We're not going to be able to be everywhere all the time. That's why it's so important for us to be able to work in concert with our allies.

Let's take the example of Darfur just for a moment. Right now there's a peacekeeping force that has been set up and we have African Union troops in Darfur to stop a genocide that has killed hundreds of thousands of people.

We could be providing logistical support, setting up a no-fly zone at relatively little cost to us, but we can only do it if we can help mobilize the international community and lead. And that's what I intend to do when I'm president.

BROKAW: Senator McCain, the McCain Doctrine, if you will.

MCCAIN: Well, let me just follow up, my friends. If we had done what Senator Obama wanted done in Iraq, and that was set a date for withdrawal, which General Petraeus, our chief -- chairman of our Joint Chiefs of Staff said would be a very dangerous course to take for America, then we would have had a wider war, we would have been back, Iranian influence would have increased, al Qaeda would have re- established a base.

There was a lot at stake there, my friends. And I can tell you right now that Senator Obama would have brought our troops home in defeat. I'll bring them home with victory and with honor and that is a fundamental difference.

The United States of America, Tom, is the greatest force for good, as I said. And we must do whatever we can to prevent genocide, whatever we can to prevent these terrible calamities that we have said never again.

But it also has to be tempered with our ability to beneficially affect the situation. That requires a cool hand at the tiller. This requires a person who understands what our -- the limits of our capability are.

We went in to Somalia as a peacemaking organization, we ended up trying to be -- excuse me, as a peacekeeping organization, we ended up trying to be peacemakers and we ended up having to withdraw in humiliation.

In Lebanon, I stood up to President Reagan, my hero, and said, if we send Marines in there, how can we possibly beneficially affect this situation? And said we shouldn't. Unfortunately, almost 300 brave young Marines were killed.

So you have to temper your decisions with the ability to beneficially affect the situation and realize you're sending America's most precious asset, American blood, into harm's way. And, again, I know those situations.

I've been in them all my life. And I can tell you right now the security of your young men and women who are serving in the military are my first priority right after our nation's security.

And I may have to make those tough decisions. But I won't take them lightly. And I understand that we have to say never again to a Holocaust and never again to Rwanda. But we had also better be darn sure we don't leave and make the situation worse, thereby exacerbating our reputation and our ability to address crises in other parts of the world.

BROKAW: Senator McCain, thank you very much.

Next question for Senator Obama, it comes from the F section and is from Katie Hamm (ph). Katie?