An eighth round of talks in Vienna to save the Iran nuclear deal is at a pivotal point, with a breakthrough close but the risk of a breakdown equally near. At a time of mounting geopolitical pressure centred on big power rivalry over Ukraine and Taiwan among a growing roster of issues, revival of the pact would be welcome for a Covid-weary world. China, Russia and their European partners have brought Washington and Tehran to the brink of an agreement that would help calm tensions in the Middle East. Flexibility and compromise are now essential if an accord is to be attained. A narrow window of opportunity exists, put at risk by potential conflict over Ukraine with military movements by the United States, other Nato countries and Russia threatening to divert attention. US President Joe Biden wants to revive the deal his predecessor and fellow Democrat Barack Obama forged in 2015 to prevent Iran from developing nuclear weapons, which Republican leader Donald Trump abruptly withdrew from in 2018. Washington last week made a concession, promising Chinese, Russian and European firms could be given waivers from sanctions to enable involvement in some civilian nuclear activities in Iran. Tehran has so far not budged on its position that all penalties have to be scrapped before it signs a deal. The 2015 deal was not perfect; it limited Iran’s nuclear programme and allowed international inspections of facilities in return for a dropping of most Western sanctions, but did nothing about Tehran’s ballistic missile tests and involvement in conflicts in the region. Tensions in the Gulf are high, with an American warship and fighter jets deployed as a warning to Tehran after rebels it supports in Yemen fired missiles at the United Arab Emirates. Republicans oppose a deal, which could be temporary if their candidate, possibly again Trump, wins the US presidency in 2024. China and Russia, which last week moved bilateral relations to new heights, are allies of Iran and instrumental in advancing negotiations. With Tehran refusing to directly talk to Washington’s envoys, they have a crucial role in communicating positions. It is now up to the United States and Iran to take the next step and set aside animosity to forge a deal and calm regional volatility.