Meanwhile, what has happened on the ground in Natanz, and in small research labs around the country, has the United States worried. The most visible problem, though in some ways the easiest to reverse, is that Iran has ratcheted up its production of nuclear fuel over the past two years, and now possesses far more fuel than it did before Mr. Trump pulled out of the agreement. At the time, he declared that Iran would return to the table, begging for a new deal.
It never did while Mr. Trump was in office, and by late last year, according to many reports, he was seeking options from the Pentagon to bomb the country’s nuclear facilities. The Pentagon resisted, and even the biggest Iran hawk in the administration, Secretary of State Mike Pompeo, argued against military action.
If the deal is restored, most of that newly enriched uranium could be shipped out of the country, which is what happened when the first accord was put together. Far more worrying, officials said, is the scientific knowledge that Iran is steadily gaining by building more advanced centrifuges and experimenting with enriching uranium to 60 percent, just shy of what is needed for a weapon.
“The longer the nonimplementation goes on, the more knowledge we will get,” a senior Iranian official said. “If the U.S. is concerned, the earlier it comes back the better.”
In 2015, the Obama administration was able to claim that if Iran raced to produce nuclear fuel for a bomb — called a “nuclear breakout” — it would take at least a year. That time frame, officials now concede, is down to a few months.
The United States, for its part, has reportedly agreed that if Iran lives by the 2015 accord, more than 1,000 sanctions could be lifted — including on the country’s central bank. Ali Vaez, who directs the Iran project at the International Crisis Group, said the United States still had some space to offer even more sanctions relief, including on some of Ayatollah Khamenei’s close associates, and on some members of the Islamic Revolutionary Guards Corps, which the Trump administration declared a foreign terrorist organization in 2019.