Second, a race toward nuclear weapons is fraught with risks. Iran could abandon the nuclear agreement and produce as much uranium as quickly and at as high a level of enrichment as it would like. Khamenei has already announced that he has ordered preparations to “upgrade” Iran’s enrichment capacity. Iran could also decide to restart work on weapon designs and fuses, and sprint to a nuclear weapons capability without declaring that it is doing so.

But any such Iranian decision, if it became known, would most probably lead the Europeans to join the United States in imposing sanctions. Given that Washington has stated that it will not allow Iran to acquire nuclear weapons, Tehran would also be risking an attack aimed at its nuclear infrastructure (and perhaps more). The Iranians would probably also lose the support of Russia and China — at a time when some in the Iranian leadership are pushing for stronger ties with both. It appears unlikely that they would pursue this course in the near term.

Third, Iran’s calculation will certainly be shaped by assessments of the impact of U.S. strategy. It is unclear how comprehensive U.S. sanctions will be and how damaging these would be to Iran’s already weak economy. It is likely that fresh U.S. sanctions will cause significant damage by discouraging investment, encouraging further capital flight and perhaps increasing labor unrest.