Iran's President Rouhani is sincere about a nuclear deal, because the costs of building a nuclear bomb are too high. But demonizing the US is still the linchpin of foreign policy for a certain faction in Tehran. For them, normalization of US relations would mean the regime's end.
Iranians and Westerners see hope in President Rouhani's UN visit today. But even with the backing of the supreme leader, reforming Iran's economy will be a difficult task for Rouhani, especially as he must challenge the power of the Revolutionary Guard and intelligence services.