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US PRESIDENT Donald Trump has abandoned the 2015 deal that limited Iran’s ability to build nuclear weapons. Although Iran has complied with every requirement of the (JCPOA), the US won’t keep its side of the agreement: Trump plans to reimpose heavy trade sanctions.

The other parties to the deal – the UK, France, Germany, China and Russia – still support it. But the threat of US penalties is expected to massively discourage firms from trade and investment in Iran, which could cause the JCPOA to collapse.

Such a failure would have consequences beyond Iran resuming its quest for the bomb. Perceptions that the US may not honour agreements could tempt more countries to go nuclear and jeopardise other arms control deals – notably the last surviving nuclear treaties between the US and Russia.

What’s worse is that Trump’s biggest objections to the JCPOA aren’t actually valid. Under the deal, Iran is able to enrich uranium to a limited extent for use in nuclear power plants, but it cannot make highly enriched uranium, which could be used to make a bomb. Trump’s main complaint is that the stringent limits on Iran’s enrichment end in 2031 – whereupon, he says, it can resume making highly enriched uranium. But that ignores technology being developed by the International Atomic Energy Agency (IAEA) that could keep such safeguards in place beyond then.

“Perceptions that the US may not honour arms agreements could tempt countries to go nuclear”

“A lot of the JCPOA lasts forever,” says Daryl Kimball, head of the Arms Control Association in Washington DC. When extra-stringent inspections end in 2031, Iran switches back to normal IAEA monitoring rules under the Treaty on the Non-Proliferation of Nuclear Weapons. In the past that monitoring, based on infrequent inspections, didn’t stop Iran covertly enriching uranium and working towards developing a bomb.

Now, the IAEA plans to update its methods for monitoring all countries in the treaty that don’t possess nuclear weapons – not just Iran. The goal is to track the flow of uranium isotopes through enrichment plants in near-real time, as it does with its current daily inspections in Iran. For that it is developing secure, remote monitoring technology that could be ready by 2031.

One such monitoring system, developed at National Laboratory in Tennessee, has even debuted in Iran. The uses a gamma-ray detector to measure U-235 – the isotope boosted in highly enriched uranium – in the gas passing between centrifuges in an enrichment plant.

Combining these readings with temperature and pressure sensors allows the system to determine how much the gas has been enriched. The equipment could be stationed at the start and finish of an enrichment line. If it detects too much U-235, it is possible the plant is being used to create material for a weapon.

This monitor alone isn’t foolproof. “It can be spoofed by adding or removing uranium at points in the process that are not monitored,” says at Princeton University.

But Goldston and his colleagues have modelled ways this could happen and say a under development could together provide near-real time warning if a plant operator tries to break the rules.

Load monitors being would let the IAEA measure how fast uranium enters and leaves the enrichment process, says Goldston. Tools being in Richland, Washington, automatically measure the mass in cylinders of material entering and leaving the plant. Together, these could keep tabs on all the uranium passing through enrichment. Cameras with pattern recognition focused on pipework and detectors watching for unusual neutrons, gamma rays or chemical release could also reveal illicit changes to the enrichment process.

All this can be made tamper-proof using technologies the IAEA has already developed for monitoring plants that store or reprocess spent nuclear fuel, ranging from , to backup electrical power that cannot be unplugged. Data would be sent securely to the IAEA. Anything unusual could trigger an “unannounced access” inspection.

Although the technology isn’t quite ready yet, the 2031 JCPOA deadline would give the IAEA time to put a stringent monitoring regime based on these devices in place, says Goldston. But if the deal collapses, Iran will at best go back to the infrequent monitoring that allowed it to work on a bomb before – and will have little incentive to trust international promises again.

“Withdrawing from the Iran deal is a catastrophically dumb decision,” says of the Carnegie Endowment for International Peace in Washington DC, since it makes it harder to limit the spread of nuclear weapons. “It will be more difficult for the US to strike deals with future proliferators because our word cannot be trusted.”

“In three years there might be no legally binding limits on the world’s two biggest nuclear powers”

The most obvious case is Iran itself, which says it may resume bomb development. Upcoming talks between Trump and North Korean leader Kim Jong-un may also suffer – bad news now we know Kim’s warheads are 10 times bigger than the Hiroshima bomb (see “North Korea’s Mount Doom”).

More worryingly, US allies that haven’t developed their own nuclear weapons because of promised protection by the US nuclear “umbrella” may reconsider. Saudi Arabia’s foreign minister declared last week it would do just that if Iran restarts its weapons programme. Egypt or even Japan could follow. Worse still, Israel might consider using its nukes against Iran.

Trust in anyone’s nuclear promises was wobbly before the US withdrawal. The non-proliferation treaty recognised the US, UK, France, China and Russia as nuclear weapons states, but required them to negotiate cessation of the nuclear arms race and nuclear disarmament. Everyone else forswore nukes.

It worked at first. Despite widespread predictions that dozens more countries would go nuclear, only India, Pakistan, Israel and North Korea have done so. And from 1972, a series of treaties between the US and Russia cut their long-range nuclear arsenals by an impressive 85 per cent.

But efforts have stalled. Far from disarming, all nuclear states are modernising their arsenals, because they fear others’ upgrades threaten their own deterrents. In February, the called for the country to acquire its first new nuclear weapons since the cold war. It also recommended their use to retaliate against non-nuclear attacks. Russia also plans ““, according to defence minister Sergey Shoygu.

Loss of trust

That means the biggest risk from any loss of trust following the collapse of the JCPOA may come from the US and Russia, which between them hold 92 . “In three years there might be no legally binding limits on the world’s two biggest nuclear powers,” , head of the Institute for US and Canadian Studies in Moscow warned a meeting of non-proliferation treaty members in Geneva in April.

Three nuclear treaties between the countries are already dead, he said, and the remaining two are hanging by a thread. In February, Russia and the US both fulfilled the conditions of the 2010 New Start agreement, limiting them to 1550 deployed warheads each. It expires in 2021. It can be extended by five years, but talks to do that must start soon. None have been scheduled since the last meeting in November.

An extension is unlikely unless a second treaty can be saved. The 1988 Intermediate-Range Nuclear Forces Treaty bans certain ground-launched nuclear missiles. The US accused Russia of testing just such a missile in 2014, while Russia says that the US’s drones and land-based missile defence system violate the treaty.

There are ways to meet these concerns with inspections and new agreements, says Rogov. But without talks, they won’t happen. And without trust, talks could be futile. The fallout from Trump’s decision to renege on a nuclear bargain has only just begun.

This article appeared in print under the headline “The art of the deal-break”