What If...

Fallows ponders a nuclear armed Iran and what we can (or can't) do to prevent it:

...in addition to being foolish and self-defeating, a preemptive attack on Iran would be wrong, except in the specific narrow circumstances that have always been held to justify similar action against a similar potential nuclear threat from any other source: clear evidence that deterrence had failed and that an attack by the other side was imminent. True self-protective preemption, that is; not this open-ended "preventive" war of recent years.

He also flags a report on the subject.