Thomas Ricks stokes the fire.

A small group of U.S. military experts and intelligence officials convened in Washington for a classified war game last year, exploring strategies for securing Pakistan's nuclear arsenal if the country's political institutions and military safeguards began to fall apart.

The conclusion of last year's game, said one participant, was that there are no palatable ways to forcibly ensure the security of Pakistan's nuclear weapons -- and that even studying scenarios for intervention could worsen the risks by undermining U.S.-Pakistani cooperation. "It's an unbelievably daunting problem," said this participant, a former Pentagon official who asked not to be identified because of the game's secrecy. The contingency plans that do exist, he added, are at the headquarters of U.S. Central Command in Tampa, and are in "very close hold." Even so, he said, planners really haven't developed answers for how to deal with nuclear weapons stashed in Pakistan's big cities and high mountain ranges.

"The bottom line is, it's the nightmare scenario," said retired Marine Col. Gary Anderson, who participated in an earlier exercise that simulated a breakup of Pakistan. "It has loose nukes, hard to find, potentially in the hands of Islamic extremists, and there aren't a lot of good military options."