Tillerson should have known that and defaulted to Trump’s other position - scrap the deal. A deal without verification is no deal. Better no deal than a bad deal that allows Iran to build nukes.
This is where “the resistance” and Never Trumper gaslighting has done great damage. Instead of following POTUS’s agenda like a subordinate should Tillerson decided he knew better and freelanced. This was never going to end well once he did that.
Trump wanted to fix it or scrap it. Tillerson got bogged down trying to fix it when it was impossible to please all those polarized viewpoints. I don't think a negotiated settlement is possible. That deal should have been scrapped long ago. All Iran understands is force and pressure. We will see how this NK situation develops which could influence how we handle Iran.