TEHRAN, July 3 -- The fatwa is gone. Ali Khamenei's religious ruling against nuclear weapons, the one Iranian negotiators cited in every round of talks for two decades, died when he did on February 28. His son Mojtaba, elected supreme leader nine days later, has not issued a replacement. In four months in office, he has not, in any public statement, addressed nuclear weapons.

The nuclear working group resumes July 9, the week after the funeral ceremonies concluded in Tehran. The US team will be negotiating constraints on an enrichment program controlled by a man whose position on whether Iran should possess nuclear weapons remains, by every public measure, unknown.

That silence is the central structural uncertainty entering the post-cea...