JUDY WOODRUFF:

Now: two views on whether a nuclear-armed Iran makes the Middle East a safer place.

John Mearsheimer is a professor at the University of Chicago. He's a West Point graduate and former Air Force officer. And he's written extensively on strategic issues. Dov Zakheim served in the Pentagon during the administrations of George W. Bush and Ronald Reagan. He's now a senior adviser at the Center for Strategic and International Studies.

And, gentlemen, thank you both for being with us.

John Mearsheimer, I'm going to start with you.

This all did start with that article in "Foreign Affairs" magazine by Kenneth Waltz. You don't go as far as he does in arguing that a nuclear-armed Iran would be a net positive. But you do agree with him that it would bring stability to the region. Why?

JOHN MEARSHEIMER, University of Chicago: I think there's no question that a nuclear-armed Iran would bring stability to the region, because nuclear weapons are weapons of peace. They're weapons of deterrence.

They have hardly any offensive capability at all. And if Iran had a nuclear deterrent, there's no way that the United States or Israel, for that matter, would be threatening to attack Iran now, in the same way that if Saddam had had nuclear weapons in 2003, the United States wouldn't have invaded Iraq, and if Libya had nuclear weapons in 2011, the United States wouldn't have gone to war against Libya.

So I think that if you had a Middle East where other states besides Israel — and this, of course, includes Iran — had a nuclear deterrent, it would be a more peaceful region. But the problem is that there is always some small possibility that there will be nuclear use.

And the most likely scenario is what's oftentimes referred to as inadvertent escalation. And this is where you have a conventional war that starts off with no intention of turning into a nuclear war, but inadvertently escalates to the nuclear level.

And you can hypothesize all sorts of situations, for example, where a conventional war between India and Pakistan, which both have nuclear weapons, escalates from the conventional to the nuclear level. And, of course, the same logic applies to the Middle East.

There's only a small, a very small possibility that that would happen. But that small possibility is enough to make me very wary of the idea of Iran acquiring nuclear weapons.