John F. Kerry and Ernest Moniz write: When President Obama took office, he faced an Iran that had mastered the nuclear fuel cycle, had constructed a covert uranium enrichment facility inside a mountain, was on its way to installing nearly 20,000 centrifuges for uranium enrichment, was developing advanced centrifuges and was building a heavy-water reactor that could produce weapons-grade plutonium. If Iran wanted to develop a nuclear weapon, it was already well down that road and the international community had little insight into its program. Against this backdrop the president vowed never to let Iran obtain a nuclear weapon.

The deal reached in Vienna this month is not only the best way to prevent Iran from having a nuclear weapon, it is the only durable and viable option for achieving this goal. This comprehensive diplomatic resolution has the unified support of the world’s leading powers. It extends the time Iran would need to develop a nuclear weapon, provides strong verification measures that give us ample time to respond if Iran chooses that path, and takes none of our options off the table.

Specifically, the deal blocks each of Iran’s possible pathways to producing fissile material for a nuclear weapon: the highly enriched uranium and the plutonium production pathways, as well as the covert pathway. This deal is based on verification, not trust. Before obtaining significant relief from economic sanctions, Iran must roll back its enrichment, its research-and-development and its stockpile of enriched uranium. To preclude cheating, international inspectors will have unprecedented access to Iran’s declared nuclear facilities, any other sites of concern and its entire nuclear supply chain, from uranium production to centrifuge manufacturing and operation. [Continue reading…]