Iran is an entirely new proposition - they don't adhere to MAD because they think the Last Imam is coming any day now and the world is going to end, and they will be happy to help it along. A jihad terrorist could carry one of Iran's nukes into Greenville and detonate it at Bob Jones University.
Greenville is not a logical target (you'd think a military installation or something financial would make more sense) - but as far as striking terror into ordinary Americans, the illogicality of it would be an effective tool.
And the Iranian government is just nutty enough to try something of the kind.
At the end of WW II—as Patton crossed the Rhine into the Fatherland—Adolph Hitler ordered that the SS mount poison gas on V-2 Rockets and launch them at the advancing Americans. The rockets were readied but a German general said no and it was never done. There may be some generals in Iran who are not willing to see their nation bombed into a nuclear wasteland. They are not all fanatics willing to die for an abstract idea like the 12th Iman.