No president can anticipate all of the problems that will arise on his "watch," but surely even his worst enemies will admit that George W. Bush has been handed more than his fair share of exploding cigars. To be sure, observers have long foreseen that a time would come when an alarming number of medium-sized nations would acquire the ability to construct nuclear weapons and the technology to inflict them on other countries. Hence the decades-long effort to impose restrictions on such efforts, notably through the Nuclear Non-Proliferation Treaty. But the treaty has been only marginally successful, and a series...