President Trump, who has never made a secret of his hostility toward Iran, called recently for a grand regional strategy among Sunni nations to isolate the country. But Tehran received that threat with surprising equanimity because, in practice, the Trump administration has shown a willingness to do business with the country.

On the surface, it looked as if there was a lot of bad news recently for the Islamic Republic. At the recent Arab-American summit meeting in Saudi Arabia, Mr. Trump was the guest of the Saudi king, Salman bin Abdulaziz al Saud, a sworn enemy of Iran, and the countries signed a record-breaking $110 billion arms deal.