… Whatever Mr. Obama may say, the point of this nuclear deal isn’t just to postpone the Iranian acquisition of nuclear weapons by 10 years. For it to be more than a mere deferral, it also must improve the relative strategic position of the U.S. and its allies so that by 2025 they will be in a stronger position to stop Iran from entering the club of nuclear-armed powers. How might the U.S. achieve this?

As the president put it, his “hope is that building on this deal, we can continue to have conversations with Iran that incentivize them to behave differently in the region, to be less aggressive, less hostile, more cooperative . . . in resolving issues like Syria or what’s happening in Iraq, to stop encouraging Houthis in Yemen.” His goal by the time he “turn[s] over the keys to . . . the next president, is that we are on track to defeat ISIL . . . that we have jumpstarted a process to resolve the civil war in Syria, [and] that in Iraq . . . we’ve also created an environment in which Sunni, Shia and Kurd are starting to operate and function more effectively together.”

This echoes Mr. Obama’s illuminating account of his strategy for the Middle East to the New Yorker magazine in January 2014. “It would be profoundly in the interest of citizens throughout the [Middle East] if Sunnis and Shias weren’t intent on killing each other,” he mused. And “if we were able to get Iran to operate in a responsible fashion—not funding terrorist organizations, not trying to stir up sectarian discontent in other countries, and not developing a nuclear weapon—you could see an equilibrium developing between Sunni, or predominantly Sunni, Gulf states and Iran.”

In short, for all the high-flown rhetoric of the president’s speeches, his goal is the classic realist objective of a balance of power in the region. The technicalities of the Iran deal—the number of centrifuges, the size of the enriched-uranium stockpile, the rigor of the inspections regime—need not detain us here. The key question is whether or not slowing down Iran’s nuclear program will increase regional stability. Critics of the deal should acknowledge that it might, for in the realm of conjecture there are no certainties. But the president and his advisers should admit that the probability is very, very low…