t is very difficult to imagine a scenario in which the US would be willing to go to war with Iran. Iran is a militarily-powerful state that is capable of putting up an excellent fight against the US. It's nuclear facilities are deep underground, where bombing cannot harm them. They are capable of closing the Straights of Hormuz even if they are invaded.
On the bit about not being able to hit the underground facilities - I'm not sure that's a given. After all the US has known about this and had lots of time to work around it. No one expected the stealth helicopter raid into Pakistan to nab OBL, or the Stuxnet virus but they were systems that were developed in secret and successfully deployed. So I would assume hitting bunkers is a problem our massive military industrial complex is looking into with some sort of workable solution. The X-37B, for example, is perfect for delivering a Rod From God from orbit, which *might* do the trick. Not that I would know about that or any other solutions. I just don't believe that the military doesn't have
any solutions.
As for Iran being able to defend itself, oh sure, they're more capable than Iraq or Afghanistan. But until they are able to figure out how to take down B-2's, F-22's, tomahawks and stealth drones, I'm not sure how much they'll be able to thwart a bombing raid. Now they could conceivably launch cruise missiles at our ships and mine the Straight of Hormuz, but even then success in either of those endeavors are far from ensured. We've been preparing for those eventualities, would have allies from at least Israel, presumably, and even going it alone could bring overwhelming power to bear.
Granted, all of those things I think are highly unlikely. But that doesn't mean the Iranians want to have to deal with that eventuality if they can avoid it, which it now appears they can avoid it altogether and crucially, are willing to do through negotiation. Then there's the prospect of sanctions being dropped and possibly even for relations to be normalized. So they have a carrot and a stick and even if the stick isn't very credible, it's still there.
What is really a shame is that this situation has come to pass to begin with. We should have tried to make amends after the hostages were released in '80. I can't really see any reason why we shouldn't have, though of course the Iranians haven't always been willing to make amends with the US either.