It would be really ironic, and not out of the question, if Obama, after trying so hard to avoid war with Iran over nukes, might wind up being forced to go to war with a nuclear-equipped, Taliban/Al-Quaeda-led Pakistan. What's really scary is that taken out Paki nukes might itself require nuclear weapons, and nuclear-capable Russia, China and India (and maybe Iran, too) might not be very happy with a theater nuclear conflict breaking out so near their borders.

A nuclear attack on the US or its allies (even an unsuccessful one) would make it almost impossible for the US not to respond in kind. And the N Koreans know this, too.