He wants the removal of the agreement’s sunset clauses, curbing of Iran’s ballistic missile program and regional influence, and more intrusive inspections of Iran’s nuclear and military facilities. Tehran has rejected any renegotiation of the signed multilateral agreement, which continues to be backed by the other four permanent members of the UN Security Council, plus Germany.

The JCPOA materialised after nearly two years of hard-hitting negotiations. The US and Iran had to move substantially from their original positions. Washington abandoned its insistence on Iran foregoing its entire nuclear

program, and Tehran gave up its resolve to continue its uranium enrichment at a high level. Tehran also agreed to allow expanded IAEA oversight, to reduce dramatically its stockpile of enriched uranium and its centrifuges, and not to build heavy water nuclear reactors for the next 15 years. In return, the other signatories agreed to lift all the nuclear-related sanctions against Iran.

The UN Security Council unanimously adopted Resolution 2231 endorsing the agreement on 20 July 2015, lifting all UN sanctions. The US supported the resolution, but maintained sanctions linked to alleged Iranian support of terrorism and human rights violations.

The nuclear deal has had strong American, regional and Iranian critics prior to – and after – its conclusion. Trump’s opposition is fanned by Iran’s two regional rivals, Israel and the Kingdom of Saudi Arabia.

In Iran, President Hassan Rouhani’s conservative opponents, who dominate most of the levers of power, have opposed any opening up to the US. They regard the US as a hegemonic power with a history of interventionist attitudes towards oil-rich Iran. They cite America’s overthrow of the elected nationalist government of prime minister Mohammad Mossadegh in 1953, and its support for the pro-Western Shah to rule Iran at the US’s behest for the next 25 years and threats to change the Iranian Islamic regime to make their case.

Trump’s decision to scrap the agreement in defiance of the advice of his Secretary of Defense, and America’s European and non-European allies, including Australia, could have serious implications.

It would cause a mortal blow to non-proliferation and the credibility of the US as a reliable negotiator, giving more reasons for a state like North Korea to remain distrustful of it in reaching a negotiated settlement on its nuclear status. It would also send a wrong message to most other countries, including America’s core allies, which have already been bruised by a number of Trump’s impulsive policy actions.

It would embolden Iran’s regional adversaries, especially Israel and Saudi Arabia, to continue to treat Iran as enemy No. 1, while obscuring how their behaviour has also contributed to regional volatility.

Further, it would open up more space for Russia and China to fill the gap in world leadership at a cost to the US.

It also stands to affect the texture of the Iranian domestic political scene by assisting the hardline cluster to undermine President Rouhani and his supporters. Given their strong hold on the power structure, they could engage in responses that could lead to a military showdown with the US and its regional allies, with debilitating consequences for not only Iran, but its neighbourhood and American interests in the area.

The Islamic Republic has built sufficient hard power capability and a regional network of activist groups, and an asymmetrical warfare strategy to make any attack on it very costly for its perpetrator. Despite their political divisions, the Iranian public could be expected to unite behind their government as they have repeatedly done in the face of external hostility in the past.

The risks associated with cancelling the nuclear agreement are far greater than keeping it in place. Tampering with it could set in motion an uncontrollable chain of events.

Amin Saikal is distinguished professor and director of the Centre for Arab and Islamic Studies at the Australian National University, and author of Iran Rising: The survival and future of the Islamic Republic (Princeton University Press, 2018) – forthcoming.