Even then, the deal was widely criticized as too weak by many in Congress and by Israel, which saw Iran’s possible reach for a nuclear weapon — an aspiration always denied by Iran — as an existential threat.
After Mr. Trump restored American sanctions, the Europeans tried to keep the deal alive, but proved unable to provide Iran the economic benefits it was due under the deal’s terms. The American sanctions, based on the global power of the dollar and the American banking system, kept European and other companies from doing business with Iran, and Mr. Trump intensified the pressure by adding many more sanctions.
Iran responded in various ways, including attacks on shipping and on American allies in Iraq, but more important by restarting uranium enrichment at a higher level and with centrifuges banned under the deal.
The estimated time it would take Iran to make enough enriched uranium to produce a nuclear weapon has now shrunk from a year, which was what the deal wanted to preserve, to just a few months. Iran is also making uranium metal necessary for a warhead, also banned under the deal, and is aggressively supporting allies in the Middle East, including many the West regards as terrorist groups.
In a further pressure tactic, Iran has interpreted the inspection requirements of the deal narrowly, and has declined to answer questions from the International Atomic Energy Agency about radioactive particles that inspectors found at sites that have never been declared by Tehran as part of the nuclear program.
In late February, Iran agreed to keep recording information on its inspection equipment for three months, but without granting I.A.E.A. access. If economic sanctions are not lifted in that time, Iran says, the information will be deleted. That would leave the world in the dark about key parts of the nuclear program.
Iran insists it can return to compliance with the deal quickly, but wants the United States to do so first. The Biden administration says it wants Iran to go first.