For decades, the debate on Iran in the United States has been dominated by a legend in which an elderly aristocrat plays the central role. The legend is that in August 1953, a couple of CIA operatives organized a coup d’état that toppled a democratically elected government and paved the way for the seizure of power by the mullahs 26 years later. The hero of the legend is one Muhammad Mossadegh, who had been appointed prime minister by the shah for a second time in 1952.

The legend was born almost a decade after the events, when the CIA, its reputation …