It is a law of arms control: Significant agreements are impossible until they are unimportant, which means until they are not significant. If Denmark wanted nuclear weapons, we would consider that nation daft but not dangerous. Iran’s regime is malevolent, but there are polls (how do you poll in a theocratic police state?) showing substantial support for the nuclear-weapons program and ballistic-missile development. The median age in Iran is 30.3 years (in the United States: 38.1; in the European Union, 42.9). The nation is more porous to outside influences than can suit the regime, which has a despotism’s normal preference for intellectual autarky. So, buying time was not a negligible goal for the original deal — or for whatever comes next, if anything does.

It is condign punishment for Obama that his signature foreign-policy achievement, the deal with Iran, could be so casually jettisoned. It should have been a treaty. If it were, it would have enjoyed more public support and could not have been erased by what created it — presidential unilateralism. Obama’s successor might learn from this when — if — he produces an alternative plan for a slightly more distant and less dangerous future.