Reagan had a point. His inclination to negotiate with the Evil Empire left many of his conservative friends aghast. In an otherwise touchingly affectionate assessment of the 40th president's tenure, my Washington Post colleague George Will said that Reagan had "accelerated the moral disarmament of the West ... by elevating wishful thinking to the status of political philosophy."

Further right, the conservative activist Howard Phillips accused Reagan of being "a very weak man with a very strong wife and a strong staff" who had become "a useful idiot for Kremlin propaganda." Wow!

Few metaphors are perfect; Iran is not the Soviet Union. But the Reagan legacy is worth pondering to understand why, barely hours after the nuclear deal with Iran was announced, so many of President Obama's critics leapt to conclude that the accord, as House Speaker John Boehner said, would "only embolden Iran—the world's largest sponsor of terror." Many of the president's supporters were just as fast off the mark in backing him.