The diplomats who negotiated a nuclear deal with Iran always knew that if they succeeded, it would come under heavy scrutiny.

Four days after a deal was announced, it is becoming increasingly clear that they are getting what they bargained for. Since the agreement was announced Tuesday, much of the reaction has been critical and some downright hostile, as Republican presidential candidates, conservative pundits and even some U.S. allies in the Middle East have challenged what was achieved.

After nearly two years of intense, and largely secret, negotiations, the Obama administration has started a new phase of defending the deal that could determine whether Congress will approve it after a 60-day review.

As officials from President Obama on down publicly praise the accord and describe it as the best available alternative to war, behind the scenes, the administration is briefing nuclear and nonproliferation experts on its complex details in hopes that they will back it and share their views with skeptical lawmakers and the American public.

Political proponents and critics of the agreement are looking to these experts for help in understanding the strengths and vulnerabilities of a 109-page document that includes five highly technical annexes.

Many experts praise the agreement, saying it opens Iran’s nuclear program to an extraordinary degree of intrusive inspections and constrains important elements for 10 to 15 years — and in some cases, longer.

“If you want to give the international community decent tools to reduce the chances of Iran getting a nuclear weapon, it’s a great deal,” said Jeffrey Lewis, who runs the East Asia program at the Center for Nonproliferation Studies and writes a widely read blog called Arms Control Wonk.

But others have questioned whether the agreement does much to deter Iran in the long-term.

“This isn’t a deal that prevents a nuclear Iran,” said Blaise Misztal, head of the national security program at the Bipartisan Policy Center. “It’s a deal that prevents a nuclear Iran for 15 years.”

‘Does it cure cancer? No.’

The divergent opinions reflect the compromises made to secure a deal between Iran and the six world powers it negotiated with — the United States, Britain, France, Russia, China and Germany. Though Iran has always insisted that its nuclear program is for peaceful energy production, the West imposed sanctions when it believed that Iran was seeking to build nuclear weapons.

“We can argue about the deal,” said a Western diplomat, speaking on the condition of anonymity about the closed-door negotiations that led to a breakthrough in deadlocked talks. “But it does what we set out to do. It blocks Iran from elements that could lead to a nuclear weapon.

“Does it cure cancer?” he added. “No, it doesn’t. . . . It’s not a perfect outcome. But this was the deal we could do.”

What's next for Iran after the nuclear deal

One of the most common criticisms made by experts involves the agreement’s duration. In return for sanctions relief, Iran agreed to 15-year restrictions on uranium-enriching centrifuges and on the size of uranium stockpiles for use in energy production and for medical purposes. Iran also agreed to use a special “procurement channel” for all its nuclear-related needs for 10 years, with every item approved in advance. Eventually, though, those conditions would be eased.

“All Iran has to do is take the patience pathway to a nuclear weapon,” said Mark Dubowitz, executive director of the Foundation for Defense of Democracies and a sharp critic of the deal even before its completion.

Others argue that even if the United States and its partners wanted to remove all nuclear capability from Iran, they don’t have the authority to do so under international conventions. The Nuclear Non-Proliferation Treaty, to which Iran and 190 other nations are party, does not give signatories a right to enrich uranium, but it not does prohibit it, either.

U.N. Security Council resolutions that levied sanctions against Iran amid suspicions that it was seeking a bomb initially called for all nuclear activities to stop, said George Perkovich, who researches nuclear strategy and nonproliferation at the Carnegie Endowment for International Peace. But the resolutions, he noted, “didn’t say forever.”

Supporters of the agreement say the United States and its negotiating partners never had a chance of completely halting Iran’s nuclear program, launched in the 1950s with U.S. help. When negotiations to roll back the program began 12 years ago, Iran had fewer than 200 uranium-
enriching centrifuges. By the time the administration helped restart the lagging multinational talks in 2013, Iran had almost 20,000, though most use outdated technology from the 1970s.

“The day [Obama] walked in . . . Iran was already a nuclear threshold state,” said Robert Einhorn, a senior fellow with the Arms Control and Non-Proliferation Initiative at the Brookings Institution. “Full rollback, to zero centrifuges, was not a realistic or obtainable objective.”

But Einhorn agreed that the new restrictions on centrifuges, stockpiles and nuclear research are good only until they expire. Once Iran can start installing more modern, efficient centrifuges, the “breakout” time — how long it takes to amass enough material to build one nuclear weapon — will start to decrease.

“The deal stands up very well as a barrier to proliferation . . . for up to 15 years,” he said. “Beyond that, Iran will clearly be able to increase its enrichment capabilities and will be able to shorten the breakout time.”

Concern about inspections

Also coming under criticism is the way inspectors from the International Atomic Energy Agency will have to negotiate “managed” access to sites where they suspect nuclear research may be going on secretly. That can take up to 24 days — long enough, critics say, for Iran to hide evidence that it is conducting nuclear research.

Many experts say that Iran can’t cover up any serious nuclear work — especially using radioactive material that leaves an indelible and easily detected trace. Twenty-four days “might seem like a long time,” said Trevor Findlay, an expert on IAEA inspections with the Belfer Center for Science and International Affairs at Harvard University. “But in the meantime, that facility will be watched with hawk eyes.”

William Tobey, a Belfer Center scholar who was involved in nuclear talks with North Korea, argued that satellite intelligence is not infallible and that Iran can explain away any remaining traces of fissile material.

“A cleanup wouldn’t have to be perfect,” he said. “Just good enough to create doubt.”

Although the agreement says sanctions can be “snapped back” into place if Iran is caught cheating, that would effectively end the agreement, because Iran then has the right to stop complying. It’s a clause Dubowitz calls the “nuclear snapback.”

“For Iran, it’s just a question of when do they play that card,” he said.

But Kelsey Davenport, head of nonproliferation policy at the Arms Control Association, said that is not an easy out for Iran.

“The cost for that abandonment will be extremely high,” she said. “The international community will remain united trying to prevent Iran trying to run back down a path to nuclear weapons development. In a cost-benefit analysis, there really are few benefits to Iran if the deal dissolves under that sort of scenario.”