Three years ago, the Guardian welcomed the Iran nuclear deal as a triumph of diplomacy. Though sceptics doubted its value, Iran has complied with its terms – surely a vindication of the patient, painful work invested in it. Yet the agreement has never had a chance to fully mature; and now it is on life support, in the words of one expert. Donald Trump’s visceral hostility to any success attached to Barack Obama’s name, and the hawkishness of those around him, made America’s withdrawal this spring all but inevitable. Now the US administration has reimposed blanket sanctions and will turn up the heat again in November with banking and oil restrictions.

The resistance of the EU and especially the “E3” signatories (Germany, France and the UK) is welcome. The question is whether it can save the deal. No one suggests that it is perfect – but it was the best reachable. Now the circumstances are worse: Iran is a stronger force in the region and the moderate president Hassan Rouhani has lost credibility domestically because the deal barely survives. So few believe that an improved agreement is in sight, and though the US administration denies that its real goal is engineering regime change, both its comments and actions suggest otherwise.

The Iranian regime is guilty of grotesque human rights abuses at home, as well as supporting Bashar al-Assad in Syria. But sanctions are no way to support the legitimate demands of the Iranian people, who are already struggling. The rial has halved in value since April. The prices of essential goods, including medicines, have shot up. This year has already seen demonstrations unprecedented since the 1979 revolution: spurred by anger over issues ranging from high prices to water shortages. Other protesters – such as the women resisting the compulsory hijab rules – are frustrated at the lack of social and political freedoms, due to the supreme leader Ayatollah Ali Khamenei’s utter intransigence. Raised expectations have been dashed decisively: the promised economic dividend from the deal never really materialised and now looks more like a mirage.

But the lessons of the US- and UK-backed coup of 1953, which paved the way for 1979’s Revolution, should be a potent reminder of the perils of intervening in Iran’s domestic politics for US national interests; and Iranians are already painfully aware of what regime change has meant for the wider region. The Trump administration’s policies, rhetoric and outright threats are less likely to further reform and more likely to strengthen nationalism and hardliners, giving the Revolutionary Guards a greater role, whether formally or behind the scenes.

Europe’s leaders are well aware that they are in treacherous waters. There are serious doubts about whether the EU’s use of a “blocking statute” – designed to mitigate the impact of the US’s secondary sanctions on European companies doing business in Iran – will have much effect. An EU plan to use the European Investment Bank to keep money flowing has already been questioned by the bank itself, which fears it would be unable to raise money in US markets. Finding ways to give businesses the confidence and ability to trade and invest is extremely challenging, but political commitment will be ineffective unless backed by such concrete measures.