So Obama’s exasperation is understandable, but it does not bolster his argument. This Obama will brook no disagreement, accommodate no uncertainty as to the correct result. “So this deal is not just the best choice among alternatives — this is the strongest nonproliferation agreement ever negotiated,” he said at American University.

This Obama does not grant the legitimacy of his opponents’ concerns; he questions their bona fides in expressing them. “Many of the same people who argued for the war in Iraq are now making the case against the Iran nuclear deal,” he observed.

And he misleadingly overstates the case when he contends that the deal “permanently prohibits Iran from obtaining a nuclear weapon.” Yes, in the dictionary sense of “formally forbid by law, rule, or other authority.” But not in the actual sense of stopping Iran from obtaining a weapon if it is determined to do so once the agreement expires.

The best argument for the deal is, simultaneously, the most infuriatingly circular: Support this agreement because at this point no other alternative is or can foreseeably be available.