It was always going to be difficult making an agreement with Iran The IRGC and the national government have different goals.
Iran's government loves the nation - their home - and knows it to be beaten. They want to make a deal to save what's left of it for their friends, relatives, and countrymen.
"Iran" isn't even a part of the Islamic Revolutionary Guard Corps' name. The IRGC is a cause or crusade, not a nation. Has Iran been a useful and convenient host? Yes. Is Iran essential to IRGC goals going forward? Maybe not.
Try this analogy - Catholicism and Italy. If something awful happened to Rome, or to all of Italy, Catholicism would continue. Would Catholics give up their faith to save Italy? No one would expect them to do so. Why expect the IRGC to give up their cause to save Iran?
The IRGC commitment is to Shia Islam's political goals, which it views as essential precursors to its religious goals. Without nuclear weapons they cannot win, giving up the progress made toward nukes is giving up their cause, and without their cause, Iran has little value to them.
Convincing patriotic Iranians their country should give up fighting everyone and, as Trump has asked, become a normal nation is doable. Trump likely has done that.
Convincing IRGC zealots to give up their cause is orders of magnitude harder. I remain unconvinced that has been done, and wonder if it can be done.