Or take cooperation on Afghanistan. The US has encouraged Asian countries to support the government of President Ashraf Ghani in Afghanistan, principally through economic aid and investment, training (in the case of India) of Afghan security forces, and focusing international attention on regional counterterrorism priorities. Regional players recognise the importance of Iran’s participation in negotiations on the future of Afghanistan, like the Heart of Asia ministerial meetings. Support for a stable political order in Kabul will be difficult if the United States and Iran enter a crisis. For example, geography has limited India’s ability to direct resources to Afghanistan – hence, investments in the Iranian port of Chabahar to allow for the transit of Indian goods to Afghanistan, which would be undermined if the US tries to reassert crippling economic pressure on Iran.

A breakdown in Iran’s relationship with the international community also imperils India and China’s energy interests. While US energy exports to Asia provide valuable supply diversification to Asian buyers, many states want to engage with Middle Eastern suppliers, who are geographically closer, low-cost producers. Asian customers significantly reduced oil imports from Iran to comply with US sanctions under the Obama administration. They took part in a multilateral economic pressure campaign on Iran to help facilitate the diplomacy that produced the deal. The potential reimposition of sanctions would force these countries to weigh their economic needs against avoiding the anger, and sanctions penalties, of the US.

Walking away from the Joint Comprehensive Plan of Action will erode the credibility and utility of the non-proliferation regime. China is a party to the deal because of its concern that nuclear proliferation in the Middle East be checked. China’s investments in Central and South Asia would be undermined by the addition of a nuclear-weapons-capable Iran. This would have potential spillover effects for the nuclear tensions between Pakistan and India. India has relied on the US acting as an honest broker in engagements in support of non-proliferation issues and stabilising tensions with its neighbour. India’s partial reintegration into the legal nuclear club was directly facilitated by the US, and the process was highly controversial. Without the plan of action, India will feel isolated by a US government that so directly bucked a powerful arms control agreement.

Killing the deal will dramatically undermine the prospects for nuclear diplomacy with North Korea. Both South Korea and Japan have spoken about the eventual need for negotiations over the Kim regime’s nuclear weapons capability. That process, which appears remote amid current tensions, will be made even more distant if Washington ends the 2015 Iran deal. The US has a security role to play in East Asia and will lack credibility to reassure treaty allies and Pyongyang about Washington’s willingness to stick to an arms control agreement.

Given the downsides of breaking the deal, it’s no surprise that, Japan, South Korea, India and China have offered clear public support for the deal. On the sidelines of the UN General Assembly in September, Prime Minister Shinzo Abe reinforced Japan’s support for the deal to Iranian President Hassan Rowhani. The September 2017 BRICS Summit joint statement included a specific endorsement of the agreement, calling on all parties to enforce the Iran nuclear deal. The recent EU-India summit in early October similarly endorsed the deal’s contributions to international peace and security.