One of the enduring aspects of Washington’s Iran debate is its wild oscillations between the hysteria of war and the euphoria of reconciliation.

The Islamic Republic has a new president: He smiles and pledges soothing moderation. The jaded envoys who have been struggling with the Iran issue for the past decade — a period that included Hassan Rouhani’s stewardship of the nuclear file — are suddenly optimistic.

It is important to remember, however, that the American diplomats dealing with Iran suffer from a fundamental confusion about the nature of the Islamist state. The United States is accustomed to dealing with opportunistic Arab rulers but not with clerics who take their ideologies seriously. At times, reasonable men have reached high office in the Persian theocratic state only to have their pragmatism numbed by its founding ideology. It remains to be seen whether Rouhani can transcend the obstacles that bedeviled his predecessors.

The Arab world has seen many despotic rulers whose lust for power was expressed in language of ideologies they did not fully understand. Gamal Abdel Nasser spoke of Arab socialism, while the essence of his plan was the glorification of Egypt and himself as the region’s strongman. Saddam Hussein and both Assads unfurled the banner of Baathism to justify their blood-soaked regimes, even though there is scant evidence they had read the Baathists’ turgid tomes.