“The ayatollah constantly believed that we are untrustworthy, that you can’t negotiate with us, that we will screw them,” Kerry said. “This”—a congressional rejection—“will be the ultimate screwing.” He went on to argue that “the United States Congress will prove the ayatollah’s suspicion, and there’s no way he’s ever coming back. He will not come back to negotiate. Out of dignity, out of a suspicion that you can’t trust America. America is not going to negotiate in good faith. It didn’t negotiate in good faith now, would be his point.”

Kerry also said that his chief Iranian interlocutor, the foreign minister, Javad Zarif, and Zarif’s boss, the (relatively) reformist president, Hassan Rouhani, would be in “serious trouble” at home if the deal falls through. Zarif, Kerry told me, explicitly promised him that Iran will engage with the United States and its Arab allies on a range of regional issues, should Congress approve the deal. “Zarif specifically said to me in the last two weeks, ‘If we get this finished, I am now empowered to work with and talk to you about regional issues.’” Kerry went on, “This is in Congress’s hands. If Congress says no, Congress will shut that down, shut off that conversation, set this back, and set in motion a series of inevitables about what would happen with respect to Iranian behavior, and, by the way, the sanctions will be over.”