When President Barack 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 but also 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 and its entire nuclear supply chain.

If Iran fails to meet its responsibilities, sanctions will snap back into place, and no country can stop that. If Iran tries to break out of the deal altogether, the world will have a longer time period – a year compared with two months – to respond before it could produce a bomb. We also will have the moral authority that comes from exhausting all diplomatic options.

Is this a good deal for the United States and for global security? Consider the facts.

 Without this deal, Iran could double its capacity to enrich uranium in a short time. With it, Iran must reduce that capacity immediately and sharply.

Without this deal, Iran could continue to rapidly develop advanced centrifuges. With it, its program will be significantly constrained.

Without this deal, Iran could expand its existing stockpile of enriched uranium. With it, that stockpile will be reduced by 98 percent, and it will be capped at that level for 15 years. Iran will also be required to get rid of its 20 percent enriched uranium, which is most of the way to bomb material.

Without this deal, Iran could produce enough weapons-grade plutonium each year for one to two nuclear weapons. With it, Iran will not produce any weapons-grade plutonium.

Without this deal, Iran could take the steps necessary to produce a nuclear weapon. With it, Iran is prohibited from pursuing any of these steps.

If the international community suspects that Iran is cheating, the International Atomic Energy Agency can request access to any suspicious location. Much has been made about a possible 24-day delay before inspectors could gain access to suspected undeclared nuclear sites. To be clear, the agency can request access to any suspicious location with 24 hours’ notice under the Additional Protocol of the Non-Proliferation Treaty, which Iran will implement under this deal. This accord does not change that.

Most important, environmental sampling can detect microscopic traces of nuclear activities even after attempts to remove evidence. In February 2003, the agency requested access to a suspicious facility in Tehran, and negotiations dragged on as Iran tried to remove evidence. But even after six months, tests revealed nuclear activity.

The plan approved in Vienna does not expire – it is indefinite. Some provisions are in place for 10 years, others for up to 25 years. But the transparency requirements and most fundamental obligation – to preserve the peaceful nature of its nuclear program – are permanent.

Meanwhile, economic sanctions will remain intact until Tehran has met its key commitments, which include removing the core of its reactor at Arak, disconnecting and locking away some 13,000 centrifuges and shipping most of its enriched uranium out of the country.

For the United States to back away from this deal would be a historic mistake. We would be isolated from our partners, face an unraveling sanctions regime and give Iran the ability to push ahead with its nuclear program.

A nuclear-armed Iran is a threat to our allies in the Middle East, the United States and the international community.

The president has said clearly that Iran will not get a nuclear weapon. Neither sanctions nor military action can guarantee that outcome. The solution is the comprehensive diplomatic deal reached in Vienna.