Polling data shows that the American people utterly overestimate the threat that Iranian nuclear weapons pose:

Fifty-nine percent thought Iran would use nuclear weapons against the United States, and 80 percent thought the Iranians would hand them over to terrorists to use against the United States.  More thought Iran would use the weapons against Israel -- 77 percent -- and about as many -- 81 percent -- thought Iran would give them to terrorists who wanted to use them against Israel.

I do believe that a nuclear-armed Iran is not in the best interests of the United States or the world.  However, its incredibly unrealistic to think that there is a 51% chance that Iran will use nuclear weapons against the United States.  We have enough striking power to take out the country--utterly.  They'd be fools to do so.  They are rational, if misguided actors.  We should stop them from building a bomb if we can, but this is ridiculous.