Stephen D. Mull is the University of Virginia’s vice provost for global affairs. Before he arrived on Grounds in 2018, the career U.S. diplomat served as the lead implementer of the Iran nuclear deal, formally called the “Joint Comprehensive Plan of Action,” from 2015 to 2017.
In 2018, then-President Donald Trump withdrew from the pact, meant to constrain Iran’s development of nuclear weapons technology, and pursued what his administration called a “maximum pressure campaign” of crippling sanctions that it hoped would produce a stricter and more comprehensive deal. Now the administration of President Joe Biden is exploring rejoining the agreement.
UVA Today asked Mull for his take on the talks, the challenges facing American negotiators and how a recent attack on an Iranian nuclear facility is affecting the talks.
Q. Can you give our readers an overview of the talks?
A. European, Russian, Chinese, Iranian and American diplomats are meeting in Vienna this month to explore whether it will be possible to restore the Joint Comprehensive Plan of Action on Iran’s nuclear program that the parties successfully agreed to in July 2015.

Former Ambassador Stephen Mull became UVA’s vice provost for global affairs in 2018. (Photo Dan Addison, University Communications)
Although Iran had been complying with the limits the deal imposed on its nuclear program from the start of the deal, the Trump administration decided to withdraw from it in May 2018. Specifically, the Trump administration wanted Iran to renounce the concessions it had won during the negotiations allowing it to engage in limited (and fully monitored) enrichment of nuclear fuel, agree to major constraints on its ballistic missile program and its regional activities, such as its support for Lebanese Hezbollah and the Houthi rebels in Yemen, and end involvement in the Syrian civil war in support of the Assad regime. The original agreement did not address any of those issues, which was a major reason for domestic opposition to the deal in the U.S.
Q. Did Iran remain in compliance with the agreement even after the U.S. withdrew?
A. Despite the U.S. withdrawal in 2018, Iran remained in compliance with the deal for a full year while it pressed the remaining partners to work around U.S. sanctions to accelerate the economic benefits Iran had expected (but not received) from the agreement’s promised sanctions relief.
After failing in that goal, Iran decided to ramp up pressure on the other parties of the deal, probably to increase its negotiating leverage and to increase pressure on the U.S. to re-enter the deal by systematically and increasingly violating the deal’s restrictions on its nuclear program. It substantially increased its stockpile of enriched nuclear fuel from the 300 kilograms that the agreement allowed for to more than 4,500 kilograms today; enhanced the enrichment levels of its nuclear fuel to far beyond the deal’s limits, bringing it closer to the levels necessary for nuclear weapons; and accelerated the development and use of more advanced centrifuges to permit even higher levels of enrichment.

In this 2016 Oslo photo, Mull, then the lead U.S. coordinator of the Iran nuclear deal, is seated to the left of then-U.S. Secretary of State John Kerry. Iranian Foreign Minister Javad Zarif is fifth from the left. (U.S. State Department photo)
Additionally, the Iranian government threatened to dramatically curtail inspections of its nuclear facilities by the International Atomic Energy Agency, though it has now suspended that threat until May 21, and has threatened to increase its nuclear fuel enrichment level from the current 20% to 60%. (The original deal limited enrichment levels to 3.67%; nuclear weapons require roughly 90% enrichment levels.)
Q. Does the U.S. government have any stipulations before rejoining the Joint Comprehensive Plan of Action? What is the Iranian government’s stance?
A. The Biden administration has pledged it would return to the deal in exchange for Iran’s return to full compliance first.
For their part, Iranian leaders have stated they would return to full compliance only after the U.S. removes all the sanctions it has imposed in violation of the original deal, arguing that as the U.S. was the first to violate the deal, so should be the first to return to compliance. The talks aim to sort out what degree and sequence of sanctions relief by the U.S. would be enough to induce Iran to begin bringing its nuclear program back into compliance. So far, the Iranian delegation has refused to engage directly with American diplomats at the talks, but has reportedly been constructive with European intermediaries, who shuttle back and forth between the Americans and Iranians in Vienna.