The New York Times features expert commentary this morning on scary scenarios regarding Pakistani nuclear weapons. Rolf Mowatt-Larrsen and Karen Von Hippel focus on the most dangerous scenarios, including the collapse of the Pakistani state and infiltration of the Pakistani nuclear services by the Taliban. Mowatt-Larrsen points out that the latter has already happened: Pakistan has a demonstrated inability to control elements of its nuclear development program (the AQ Khan network), and Pakistani nuclear scientists have met in the past with members of al-Qaeda and the Taliban. Ellen Laipson preaches patience; Danielle Pletka complains about strategic confusion in the United States (which is true, but rather beside the point of the series); and Parag Khanna suggests institutional reform in Pakistan.
The series is worth your precious time but doesn't effectively present any solutions to the Pakistani nuclear-weapon problem. The biggest take-away is that the United States needs to help reinforce Pakistani institutions, so that a scary nuclear-weapon scenario never develops. That's good as far as it goes, but I think that there also needs to be some thought given to the thresholds at which the United States will engage in military action to prevent the weapons from falling into Taliban hands. Such action would represent an extreme desperation measure, as it means effectively giving up on the Pakistani state. Even in the extreme scenario, there's some cause for patience as it's unlikely that the Taliban could actually use a weapon without substantial assistance from the Pakistani military. That said, I'm reluctant to rely on deterrence to control the behavior of a non-centralized, non-state actor, and I very much doubt that India, China, or Russia have much of a sense of humor about loose Pakistani nukes, either.