I think he is doing EXACTLY the right thing by backing them into a corner wherein their only option is to negotiate on OUR terms or else face financial ruin and the threat of revolution at home.
P.S. I am not asking what you DON'T want him to do.
If you have an agreement with country X regarding their _________, the terms of the agreement are actionable. Meaning that if the terms are for third country inspections of their nuke plants, you (at the very least) have someone going to the nuke plant to see what they are up to. When you back out of the agreement, you don’t have those inspections taking place. So it was patently stupid to have backed out of the deal to start with.
As far as what to do next; nothing in Iran is worth a drop of American blood. He’s doing the right thing as far as not intervening. Sort of like the kid who takes his old man’s car out for a joy ride and parks it in the lake but dives back in to salvage the little hula dancer that was affixed to the dashboard.