That aggressive tone marked a change. In recent months, Iran has seemed interested in turning down the temperature with Washington, negotiating on the release of prisoners and reducing attacks from its proxy militias on American forces in Iraq. But the calculus may have changed now that polls show Mr. Trump struggling; the presumptive Democratic candidate, Joseph R. Biden Jr., was involved in the negotiation of the 2015 deal and the Iranians may have concluded it can be reconstructed if he takes office.
“I think something has certainly changed on the Iranian side,” said Henry Rome, an Iran analyst at the Eurasia Group, a political risk consulting firm. “Certainly last summer, they assumed Trump was going to be re-elected.”
Mr. Rome said he would draw two conclusions. “You don’t want to do anything that would help Trump be re-elected. That would give him a boost they simply don’t want to chance,” he said. “It also means if they wait long enough, and they are correct that Joe Biden becomes president, then you have a much different dynamic, and a much more sustainable one.”
He rejected the idea that the Iranians, sensing that Mr. Trump is desperate, might see an advantage in negotiating an agreement with him now. “The Iranian view is that this would not be a sustainable deal, with someone as volatile as Trump,” he said.
Mr. Hook argued that the release of Mr. White, who was detained for nearly two years, was evidence that the United States can negotiate from a position of strength, noting that he was returned with “no sanctions relief, no change of policy and no pallets of cash,” the last a reference to how the Obama administration returned to Iran funds it had in the United States that had been frozen for nearly 30 years.
But he also argued that the Iranian people were losing out on an opportunity to avoid have “their national wealth squandered, in the Middle East and Venezuela,’’ places where Iran is actively providing support. In the two years since Mr. Trump left the Iran deal, Mr. Hook noted, “he has met with Kim Jong-un three times.” He did not note that those meetings have, so far, been fruitless, and Mr. Kim, the North Korean leader, has continued with his nuclear weapons program.
The report from the International Atomic Energy Agency was only circulated to a small number of nations, but leaks of its contents, ahead of a meeting of the agency in a few weeks, suggest that Iran is continuing its slow but steady accumulation of nuclear material. While it is hard to calculate with any precision exactly how many months it wold take Iran to produce enough fuel to make a single bomb, Iran’s production of material — which it says is a reaction to the United States violating its commitments to suspend sanctions — has clearly slipped below the one-year buffer that was central to the 2015 agreement.