Two and a half years ago, Iran could have produced enough enriched uranium for a nuclear weapon in two months – and that timeline was rapidly shrinking as Tehran’s nuclear program expanded unchecked. Iran was also making progress on a nuclear reactor which, if completed, would produce enough plutonium for two weapons a year, all while inspectors only had access to some of Iran’s nuclear facilities.

Today, thanks to the historic nuclear deal that the United States and its partners reached with Iran in July 2015, it would take Tehran over a year to obtain enough enriched material for a bomb. Moreover, by requiring Iran to rip out over 13,000 centrifuges and cap its stockpile of enriched uranium, the deal ensures that timeframe will remain in place for well over a decade.

As part of the agreement, a central component of Iran’s uncompleted reactor was destroyed and is being redesigned to reduce plutonium output well below anything that could be used for a nuclear weapon. For at least 15 years, the deal will prohibit its ability to separate plutonium, which is necessary for a nuclear weapon.

Stringent monitoring and verification mechanisms will keep Tehran’s nuclear activities under the international community’s microscope. The multi-layered inspections regime will cover every element of Iran’s nuclear-fuel supply chain, including continuous surveillance on key nuclear facilities. The inspections regime provides the highest possible assurance that if Tehran tried to cheat on its commitments, it would be caught. For the first time, inspectors will also be able to access any site in Iran within a time bound period if concerns about illicit nuclear activities arise. This is an unprecedented provision that allows International Atomic Energy Agency (IAEA) inspectors managed access to even military sites. Some of these monitoring mechanisms expire between 10-25 years, others will be permanent.

As John Brennan, director of the Central Intelligence Agency put it, the monitoring and verification is "as solid as you can get."

An innovative element of the agreement prevents Iran from conducting certain explosive activities and experiments that are relevant to designing a nuclear weapon. This is a permanent restriction that Tehran agreed to, going beyond its international obligations. After the IAEA found that Iran conducted activities relevant to developing a nuclear weapon in the past, these prohibitions are particularly important, because in the future, Tehran will not be able to conduct these activities and then insist that the applications were for non-nuclear purposes. If Iran is caught with its hand in this cookie jar, it will be a clear violation of deal, regardless of the reasoning or explanation.  

While the restrictions on each area of Iran’s nuclear program are critical, the agreement with Iran is more than the sum of all of its parts. Every element must be implemented to continue blocking Tehran’s pathways to nuclear weapons. 

Together, the restrictions dramatically limit Iran’s nuclear activities and the stringent monitoring and verification will ensure that Tehran toes the line of the deal. Tehran will also receive sanctions relief under the deal, which will serve as an incentive to continue complying with the deal’s provisions.

While reaching implementation day is a milestone to celebrate, Iran, the United States, and its negotiating partners cannot rest on their laurels. The deal is strong from a nonproliferation standpoint; it was endorsed by over 75 scientists and nonproliferation experts as the best means to block Iran’s pathways to nuclear weapons. However, it is simultaneously fragile. All participants must protect it against neglect or sabotage. In addition to exercising vigilance in overseeing the agreement for the next several decades, each side must maintain a commitment to the deal and not allow extraneous political differences or tensions to impact successful implementation.

Iran may test the boundaries of the agreement. It is critical that violations do not go unpunished, or the deal could be killed by a thousand paper cuts. At the same time, punitive actions for violations on both sides should be proportionate, and differentiated from technical missteps, which may occur under such a complex agreement. 

The continued, successful implementation of the deal removes an existential threat of an Iranian nuclear weapon and enhances U.S. national security. But it should not be viewed as a panacea. It will not repair the U.S.-Iranian relationship overnight, nor will it solve all of the problems in the Middle East. It may open doors to make progress on some issues, but whether or not the deal does so should not impact perceptions of its success. The nuclear deal accomplishes what it needs to – it guards against a nuclear-armed Iran for over a decade to come.

Davenport is director for Nonproliferation Policy at the Arms Control Association.