Preserving the momentum that enabled the deal will be essential for implementing it. Each side must fulfil its commitments under the accord while refraining from any provocation, particularly strident declarations of victory, which could lead its counterparts to repudiate their own.

Attention now moves from the multilateral to the domestic stage, where any attempt to renegotiate the accord will torpedo it. Thirteen years of nuclear tensions and intermittent talks to resolve them have made clear that no better agreement is possible; the only alternative to endorsing this one is renewed crisis and, potentially, an escalation that could spiral out of control. Accordingly, we urge the US Congress and Iranian Majlis to promptly review and approve this accord and the UN Security Council to endorse it.

Like all arms control agreements, the JCPOA addresses a narrow but perilous threat. It will not solve the region’s many other problems, neither the proxy wars pitting Iran against its neighbours nor the hostility that still embitters Tehran’s relations with the West. Indeed, in the short term at least, it is likely to reinforce the sense in regional capitals that Iran’s star is ascending, which could exacerbate the clashes along regional fault lines. Thus the achievement of this agreement, laudable in itself, is incomplete unless it prompts an effort by all the key stakeholders to secure a broader reduction in regional tensions with the goal of establishing an inclusive regional security framework.

Overcoming decades of animosity, both within the region and between Iran and the West, likely will prove even more challenging than reaching today’s accord. But as the past two years of arduous talks have shown, even seemingly intractable predicaments can be addressed through persistent and patient diplomacy. DM

Photo: US President Barack Obama speaks to the media during a press conference where he fielded questions about the Iranian nuclear deal, in the East Room of the White House in Washington, DC, USA, 15 July 2015. On 14 July, President Obama addressed the nation to throw his support behind the deal, hammered out in Vienna, Austria between Iran and envoys from six nations. EPA/JIM LO SCALZO