Einhorn said the Iranians will need to show results fairly quickly to keep Khamenei's backing.
"The Supreme Leader has basically given them some running room," he said. "He's skeptical it will achieve anything, but has said they can go ahead and try this moderate approach and see where it gets them. But their mandate is not infinite. I don't know if there is a time limit but they genuinely need to show this moderate approach can work."