Iran is able to smuggle in large quantities of weapons and equipment into Lebanon and Gaza with little difficulty. Once they develop nuclear weapons, they'll smuggle a few in and detonate them. Israel will be in ruins and unable to mount a serious counter strike. That responsibility will fall on the US to avenge the Israelis.

Unfortunately, Iran is a large country with difficult terrain with lots of places to hide the missiles they'll have aimed at Europe. Iran will threaten to nuke several European cities if the US responds. The Europeans will not want to lose millions for Israel, and they will use diplomatic pressure to keep Washington from attacking.

The West will appear weak, Israel will be gone, and Iran will be the champion of the Islamic world for destroying the Zionist invader and making the Infidels back down. After seeing how the West reacts, the whole Islamic world will rally around them as Ahmadinejad declares himself the Mahdi.