The interim deal struck with Iran by the "five plus one" powers shows promise for achieving the end that Iran will not wind up with a nuclear program. Whether it is the deal that will be responsible for that end depends, of course, on whether Iran was building nuclear weapons at all. If Iran does not develop nuclear weapons, we may never know whether it was the deal that brought that about.

Iran claims to the "five plus one" powers — the five permanent members of the U.N. Security Council, plus Germany — that its nuclear program is for peaceful purposes only. That hypothesis receives some confirmation from the deal, because Iran is making a substantial commitment in return for only a modest reduction in sanctions. Iran's willingness to give up so much to get so little may mean that it was not working toward nuclear weapons in the first place.

But on the assumption that Iran is working toward nuclear weapons, the deal puts a definite crimp in any such efforts. Iran says it will stop high-level enrichment of uranium and will neutralize its stockpile of uranium that it has enriched to a high level. It will install no new centrifuges, these being necessary to enrich uranium.

The West has been suspicious of Iran's activities at a nuclear reactor in the Iranian town of Arak. Iran now commits to stop any production of nuclear fuel at that facility. It will provide design information on the Arak reactor — information previously not available.

Importantly, Iran will allow inspections by the International Atomic Energy Agency much more broadly than before. Thus, the "five plus one" are not relying on Iran's word alone.

Finally, the deal is short-term only — a mere six months. The concept is to keep Iran from activity that might bring it closer to weaponry while efforts are made for a permanent deal. The International Atomic Energy Agency reported several weeks ago that Iran was already slowing production processes that held weapons potential.

If Iran violates the deal, the promised reductions in sanctions could disappear. Sanctions could be reinstated or increased.

In Congress, the many members who oppose the deal don't plan to stop trying to pass increased sanctions even now. If at the end of six months Iran is not in compliance, reinstatement of the reductions, plus even more sanctions, would almost be a certainty.

On Iran's side, it is getting only a modest reduction in the sanctions that have been crippling its economy. So its economy will continue to be crippled during the six-month period. For Iran, the deal is no free ride.

One can never ensure that a state bent on nuclear weapons will never develop them. So no matter how much Iran dismantles now, it could pick up again in the future.

States sometimes see a need for nuclear weapons to counter adversaries who have them. In the Middle East, the only state with nuclear weapons is Israel, an adversary of Iran.

A good part of the impetus for Iran to go nuclear is to become a counterweight to Israel. A focus broader than just Iran might better ensure that it does not develop nuclear weapons in the long term.

Israel has never allowed outside inspections. It has refused to sign the nuclear nonproliferation treaty. And it refuses even to acknowledge the nuclear weapons it is known to possess.

The "five plus one" countries have been silent on Israel's nuclear weapons. Pressuring Iran while giving Israel only a wink and a nod lends a political cast to the efforts. The "five plus one" countries could achieve the moral high ground — and reduce the risk of Iran going nuclear — if they committed to seeking elimination of nuclear weapons in the entire Middle East.

John B. Quigley is a professor of law at Ohio State University.