“If the president pulls back on the Iran deal, given Iranian compliance” with its terms, said Wendy R. Sherman, the chief negotiator of the accord, “it will make diplomacy on North Korea almost impossible because U.S. credibility will be shot.”

Presumably, the United States would have to make some concessions to North Korea in return for limits on its nuclear program. But why negotiate with the United States if this president or the next one can just throw out any agreement?