Almost everyone who opposes the deal President Obama has struck with Iran hotly contests his relentless insistence that the only alternative to it is war. No, they claim, there is another alternative, and that is “a better deal.”

To which Mr. Obama responds that Iran would never agree to the terms his critics imagine could be imposed. These terms would include the toughening rather than the lifting of sanctions; “anytime, anywhere” nuclear-plant inspections instead of the easily evaded ones to which he has agreed; the elimination...