Going nuclear? Iran and North Korea are the two most visible--but not the only--threats in an age when it has become easier to build and hide nuclear weapons. How will President Bush respond?

• Author: Sanger, David E.
• Position: Cover Story

During the Cold War, teachers used to drill their classes on how to survive a nuclear attack, getting them to "duck and cover" under their desks. It was a ridiculous exercise: A school desk does not provide much protection against the fearsome power of a nuclear bomb, much less against the radiation it leaves in its wake. But at least then the teachers knew who the enemy was: the Soviet Union.

Now, it's a more complicated world. The United States is the sole superpower, and Russia's nuclear arsenal seems more a quaint artifact than a direct threat. But some of Russia's nuclear materials are so poorly guarded that there is fear they could fall into the hands of America's current enemies, including Al Qaeda and other terrorist groups.

The scientist who made Pakistan a nuclear power in the 1980s and '90s, Abdul Qadeer Khan, went into business for himself and started selling nuclear technology to Iran, North Korea, and Libya, and perhaps to other countries that have not yet been found out. Khan even sold Libya the blueprints for an old but reliable bomb design.

It's not yet time to get back under the desk, but the problem is growing more and more pressing. "People understood the old Cold War threat," says Robert Einhorn, a nuclear-proliferation specialist who spent years working on the issue at the State Department. "They don't yet understand the new threat because it comes from a lot of different places."

'AXIS OF EVIL'

The most immediate threats are two of the countries that President Bush once called part of an "Axis of Evil": North Korea and Iran. Both countries have seen America's troubles in Iraq (the third "Axis" country) as an opportunity to push ahead with their nuclear programs, figuring that once they have nuclear arms, the U.S. would never risk attacking them the way it invaded Iraq. That poses a challenge to America and the rest of the world: What is the President going to do about it in his second term? What can he do about it?

Bush has said that he will rely on diplomacy, not military force, to disarm both countries. The reality is that he doesn't have a choice: Iran and North Korea are far more powerful than Iraq ever was, and have ways of striking back that Saddam Hussein could only dream about. If the U.S. attempted to destroy Iran's nuclear facilities, for instance, the country could shoot missiles at Israel or at U.S. forces in the Middle East, including Iraq. And while no one doubts that the U.S. could swiftly win a war with North Korea, that country could destroy Seoul, South Korea's capital, only 35 miles from the North Korean border, which is heavily fortified with American troops.

A NEW AND DANGEROUS ERA

If North Korea and Iran are allowed to build and hold nuclear weapons, other countries are likely to follow, making the world much more dangerous. We may, in fact, be on the leading edge of a...