|Contrary to the drivel about mad moolahs, jihadi wetdreams, and general irrationality, the drive for nukes by Iran is driven by 2 forces.
1) Deterrence against regime change
2) Leverage from which to project power
which are actually 2 sides of a single coin.
Iran is the ONLY M.E. nation that has unequivocally and overtly positioned itself as THE alternative to U.S. hegemony in the M.E.. Even Saddam was just another dog in the U.S. kennel till he tried to gobble up a fellow pup and had to be put down.
As such, there is no room for diplomacy. Diplomacy is grease to get objects past each other. But when you're talking about interferences measured in meters instead of microns, one object simply has to go.
The German ex-FM puts it very well in this recent article.
He gets it.
Under a nuclear umbrella, Iran could actually begin to fight the U.S. in Iraq on a level not seen yet(Some whole number multiple of current casualty rates in Iraq). Brittania would be sent scurrying within months. Iran also would restart revolutionary drives in Shi'a Bahrain and Eastern Saudi. Can you imagine 33% of the world's daily oil production going out due to local action? Kuwait? what Kuwait? Oh that's part of Basra now.... Again.
IOW, Iran would proceed to break the rest of the U.S. aligned M.E. quite handily. And the U.S. forces in Iraq would quite literally be lucky to get out alive.
This is what endgame looks like unless the U.S. acts within the window. But even that has unknown costs. Will Iran escalate? Does Iran have intelligence on when the U.S. has decided and pre-empts the U.S.?(Russia allegedly told Saddam when and where and he hesitated, Iran won't) Will a ground war ensue? Does Iran already have nukes?...