Much remains uncertain about the foreign policy direction President-Elect Donald J. Trump will take, but his rhetoric on the campaign trail, as well as the Iran-regime-change stance of some of his first appointees, raise concerns for the viability of the nuclear accord with Iran. Its demise would reignite a crisis that could dominate his presidency, deepen tensions in a tumultuous region and deal a hard-to-reverse blow to multilateral diplomacy. Others with a stake in preserving the agreement, particularly the remainder of the P5+1 (China, France, Germany, Russia and the UK) which, with the Obama administration, negotiated the deal, should hope for the best but prepare for the worst.

More than a year after entering into force, the 2015 Joint Comprehensive Plan of Action (JCPOA) has proven to be a success: it has effectively and verifiably blocked all potential pathways for Iran to race toward nuclear weapons, while opening the door to the country’s international and economic rehabilitation – even if the pace of recovery in the aftermath of sanctions relief has been more sluggish than anticipated. The newly-elected U.S. president, however, has been unambiguous in his condemnation of the JCPOA as fundamentally flawed. As president, Trump will have the authority to repudiate it or refrain from taking affirmative steps critical for the deal’s sustenance, e.g. periodically renewing waivers to continue suspending nuclear-related U.S. sanctions on Iran. The U.S. could even unilaterally snap back UN sanctions, notwithstanding the JCPOA’s dispute resolution mechanism, likely opposition from other P5+1 members who are highly satisfied with the agreement’s implementation so far, and absence of a legitimate basis for re-designating Iran as a threat to international peace and security after the dossier on its past nuclear activities was closed in December 2015.

Some of the accord’s Republican Party critics have warned against abrogating the agreement in such a manner, as this would surely lead the international community to squarely blame the U.S. Most agreement sceptics seem to prefer reintroducing non-nuclear sanctions to incrementally augment coercive pressure aimed at inducing Iranian leaders to discard or submit to renegotiating the accord.

The agreement could be undermined by an even lighter touch, or rather by no touch at all, since lacklustre implementation would doom it as well. Sustaining the JCPOA requires Washington’s constant good-faith management: from granting licenses in a timely fashion to allow legitimate business with Iran, issuing guidelines to clarify sanctions relief ambiguities and providing assistance in modernising Iran’s Arak heavy-water reactor (a project that the U.S. co-chairs with China), to shielding the accord from external pressures, particularly attempts by congress to obstruct implementation, for example by blocking the sale of civilian aircraft to Iran contrary to the agreement’s letter.

While it is too soon to judge the next U.S. administration, its opposition to the JCPOA appears to stem less from the implementation record than from its narrow nature: an arms-control agreement that allows an adversary to come in from the cold without altering its policies more broadly. The question of whether derailing the accord would strengthen or weaken U.S. ability to address other outstanding concerns appears an afterthought for the critics.

It is too early to predict the consequences of subverting the JCPOA. Still, several observations can be made:

• Scuttling the agreement, while Iran complies with it, would almost certainly erode, if not unravel, the international coalition that was critical in enforcing the sanctions that provided leverage for negotiations. This implies that the U.S. would be in a weaker, not stronger position to renegotiate a more favourable deal and/or to reshape Iran’s regional or domestic policies. Washington’s unilateralism also could weaken both the centrality of the U.S. financial system to the global economy and the effectiveness of sanctions as a tool of its statecraft.
   
• Iran would almost certainly retaliate by resuscitating its nuclear program. Initial complacency in Tehran about Trump – that his isolationist and transactional inclinations, desire to improve ties with Iran’s close partner Russia and prioritisation of  fighting the Islamic State would redound to its advantage – increases the risk of overreaction to U.S. attempts to undercut the deal. The parliament has mandated the government to ratchet uranium enrichment up and cooperation with UN inspectors down should the U.S. renege on the bargain. Even a softer, calibrated response would reignite the nuclear standoff and complicate future negotiations by further undermining the all-but-non-existent mutual trust. In the extreme it could provide the rationale some regime-change advocates have been looking for to justify military action against Tehran. Even if Iran were to agree to more stringent, long-term restrictions, it would almost certainly, given its discontent with the sanctions relief, demand a high price for concessions. This assumes, of course, that the incoming U.S. administration would seek marginal improvements in the accord, not Iran’s capitulation on nuclear and other issues, which years of standoff under conditions more advantageous to the U.S. never achieved.
   
• Exacerbating tensions could push Iran to double down on policies it presents as essential to its national security: the ballistic missile program as conventional deterrence and “forward defence policy” of bolstering regional partners and proxies in Baghdad, Damascus and Beirut, which ostensibly aims at deterring an attack on its soil. Thus, by destabilising the JCPOA, the new U.S. administration could usher in what it purportedly seeks to prevent: greater Iranian assertiveness, more regional instability and lower odds of resolving the conflicts in Syria, Iraq and Yemen – places where Iran is part of the problem and thus, inescapably, must be part of the solution.

It is also early to assess the new administration’s appreciation of these risks. But while it determines its policy, the other P5+1 members have an opportunity to shape its thinking and discourage and even deter it from undermining the JCPOA. They should simultaneously prepare contingency plans for salvaging the agreement if they lose the U.S., which because of the sanctions it imposed has been its key signatory. If they wait to see if the Trump policy is as damaging as they fear, they may not be able to react quickly enough to limit damage. Thus:

1. The European Union (EU) should go beyond expressing strong support for the JCPOA and revive its “Blocking Regulation” forbidding compliance with U.S. extraterritorial sanctions that lack the consent of the JCPOA Joint Commission (the seven negotiating parties and coordinated by the EU). Such legislation provides political reassurance to European companies interested in re-entering the Iranian market by extending non-recognition of U.S. judgments and administrative determinations that give effect to U.S. sanctions, and by establishing a “clawback” clause for recovery of damages incurred for alleged sanctions violations. Establishing this pre-emptive measure without prejudice to a Trump administration’s commitment to the JCPOA would send a strong signal that if Washington walks away from the deal, it will do so alone, while demonstrating to Iran that the 28 EU member states will defend the agreement.
    
2. China, France, Germany, Russia and the UK should formally announce that new unilateral U.S. sanctions deemed unjustified by the majority of the Joint Commission and that interfere with Iran’s full realisation of the benefits of sanctions relief under the JCPOA would be cause to initiate disputes against the U.S. at the World Trade Organisation (WTO) and other international courts and institutions. In the late 1990s, the EU successfully challenged U.S. sanctions with a similar approach. At the same time, these countries should continue to support Iran’s admission to the WTO.
    
3. The above initiatives should be conditioned on Iran continuing to honour its JCPOA obligations. Reinvigorating its nuclear activities and severing International Atomic Energy Agency (IAEA) access in retaliation for Washington’s efforts to gut the deal would make it impossible for others to stand up to the U.S. By the same token, a firm commitment by other world powers to stand by Iran as long as it upholds the deal could bolster those in Tehran who would advocate continuing to do so.
    
4. Equally important, Tehran should avoid provocations, whether of a technical or political nature. This means limiting technical infringements of the JCPOA, even if they do not strictly constitute material violations, such as the recent accumulation of heavy water beyond the set threshold. It is also incumbent on Iran to comply with UN Security Council Resolution 2231 (2015) by refraining from testing medium-range ballistic missiles and shipping weapons to armed groups in the region, as well as not detain dual-nationals on charges that are unacceptable on their face and could provide ammunition for the deal’s detractors in Washington.  Ultimately, the nuclear agreement – even if ostensibly firewalled from surrounding conflicts – will be sustainable only if accompanied by progress on de-escalating and resolving the region’s conflicts. If they were to opt for escalation, Iranian leaders inevitably would invite counter-escalation, eventually imperiling the JCPOA. By contrast, easing tensions with neighbours, for instance by keeping Shiite militias out of northern Iraq and using influence with the Houthis to help bring the Yemen war under control, would be a constructive approach that could help strengthen the nuclear deal.
    
5. The P5+1 and Iran should convene another meeting of the Joint Commission before the U.S. transition occurs to draw lessons from the deal’s implementation so far and clarify remaining ambiguities, especially in areas where the accord’s language lacks sufficient specificity (e.g. determining what forms of low-enriched uranium should or should not be counted toward the 300 kilogram cap).
    
6. The UN’s second report on implementation of Security Council Resolution 2231 (2015), endorsing the JCPOA, is a timely opportunity for the new Secretary-General to reinforce the message to the U.S. and the world that the agreement plays a key role in global peace and security by reinforcing international non-proliferation norms. To this end, the UN should carefully balance its report, due 16 January, to reflect not only developments related to restrictions in the resolution’s Annex B, but also progress made in implementing the JCPOA’s provisions, as outlined in Annex A.

The same calculus that brought Iran and the P5+1 to compromise after thirteen years of standoff and two years of negotiations still holds: the alternatives to this agreement – a sanctions-versus-centrifuges race that could culminate in Iran obtaining the bomb or being bombed – would be much worse. Regardless of whether the incoming U.S. administration comes to this conclusion, the countries that negotiated the deal should do their utmost to preserve it.