Wendy R. Sherman, a former State Department official who served as the lead American negotiator of the nuclear deal reached between Iran and a group of six countries led by the U.S., spoke candidly about the historic diplomatic effort at the John F. Kennedy Jr. Forum on Tuesday night.

The Iran Deal would significantly restrict Iran’s nuclear capability for the next 10 to 15 years, limiting plutonium production and uranium enrichment in exchange for sanctions relief. The international agreement has faced criticism in the U.S., but Senate Democrats blocked a Republican resolution to reject the deal in September.

“The President’s charge to all of us was that we had to make sure that Iran would not be able to obtain a nuclear weapon … that we could be assured that its program was exclusively peaceful and that we had shut down all the pathways for different materials for a nuclear weapon ... and we believe we have done that,” Sherman said at the event, which was moderated by David E. Sanger ’82, a national security correspondent for The New York Times and an adjunct lecturer in public policy at the Kennedy School of Government.

Multiple times during the forum, the discussion turned toward more controversial portions of the agreement. Sherman addressed topics ranging from the concessions to allow Iran to keep a limited enrichment program, Iran’s human rights record, and Israel’s opposition to the deal.

“We made a decision. It is a debate one can have. But the decision President [Obama] made was that a destabilized Middle East—a chaotic, a difficult, a painful Middle East—would be even worse if Iran had a nuclear weapon,” Sherman said.

“That is a strategic debate, but I agree with the president,” she added.

While Sherman said she remains hopeful that the deal is a major step forward, she acknowledged that there is still much work left to be done.

“We’re very proud of what we’ve done, but there is a very long road ahead, and this is all based on verification, on monitoring, this is not based on trust,” Sherman said. “After decades of mistrust, you don’t solve that in two years or four years. It’s going to take a substantial amount of time.”

After one of her first public appearances since leaving her position as under secretary of state for political affairs on Oct. 2, Sherman will now assume a semester-long resident fellowship at the Institute of Politics and host a study group on negotiation and diplomacy.