LONDON - Having spent months lobbying US President Donald Trump unsuccessfully over the Iran nuclear deal, European countries are now scrambling behind the scenes to save an agreement negotiated through painstaking diplomacy.
Trump is set to announce his position on the 2015 accord as early as Thursday having spent the past two years disparaging a key foreign policy breakthrough of his predecessor, Barack Obama, as "the worst deal ever."
Most analysts expect him to declare that Tehran is failing to live up to its commitments -- a view not shared by the other five world powers involved in the talks.
A decision by Trump to "decertify" the deal would leave it at grave risk with the US Congress having 60 days to decide whether to re-impose specific sanctions on Tehran that were lifted because of the diplomatic pact.
"At a legal level the deal would not -- yet -- be dead, but politically the signal is very strong," said one European diplomat speaking about Trump's expected decision to de-certify.
"This agreement is also a deal that depends on confidence," the diplomat said, asking not to be named because he was not authorised to speak publicly.
The deal, which formally took force in January 2016, was designed to stop Iran gaining atomic weapons -- an objective Tehran has always denied pursuing.
Under the deal, Tehran agreed to mothball large parts of its nuclear programme.
- Unwilling to listen? -
Trump's comments on the Iran deal have reinforced perceptions of his administration as unpredictable and deaf to the views of Europe's main powers, which have historically been America's closest allies.
Both British Prime Minister Theresa May and French President Emmanuel Macron used the United Nations General Assembly in September to try and change the 71-year-old US leader's mind on Iran -- to little effect.
"Frankly, that deal is an embarrassment to the United States," Trump told the General Assembly.
Europe's efforts recall the fruitless campaign to persuade Trump to respect the 2015 Paris agreement on climate change, which also saw concerted efforts in private and public from France, Britain and Germany.
Finding the White House impervious to their reasoning, European diplomats are now focusing their attention on members of the Republican-dominated US Congress.
"Our embassy is working with the legislature," German foreign ministry spokesman Rainer Breul said earlier this week. "We are looking for dialogue, to explain our arguments and why in our opinion the Iranian deal is a success."
- Blow to trade -
European companies have moved into Iran over the last year, keen to tap a growing and potentially lucrative market but still wary about some US financial sanctions which remain in place.
French firms have been at the forefront, with oil group Total and carmakers Renault and Peugeot announcing investments of several billion euros.
German industrial giant Siemens has also announced new deals there, while European aircraft maker Airbus bagged orders in June from two Iranian airlines for 73 planes which would be worth several billion euros.
"If Congress reimposes sanctions, I don't see many chief executives proposing to their boards 'hey, let's invest in Iran,'" said the European diplomat who spoke on condition of anonymity.
Thierry Coville, an analyst at the Institute of International and Strategic Relations (IRIS) in Paris, said he expected the Europeans to club together with Russia and China, the other two powers who helped craft the deal.
"If there are new sanctions, it's going to be very complicated," he explained.
As well as re-opening an international crisis with Iran that European countries thought had been resolved, diplomats also worry about the message sent by Trump to other states, particularly North Korea.
Tensions have soared between Washington and Pyongyang, a secretive and totalitarian state that insists it needs to develop an atomic weapon to defend itself against US aggression.
"The message you give if you don't stick to the agreement would be: don't negotiate, don't negotiate with the West particularly, because agreements are not honoured," said another senior European diplomat on condition of anonymity.
David Patrikarakos, a journalist and author of the book "Nuclear Iran: The Birth of an Atomic State", said that the 2015 deal was "that rarest of things: a concrete result of European unity."
"One thing is clear. Even if Trump were to withdraw, it would not necessarily spell the end of the deal. The EU will fight alongside Iran's moderates to keep it alive," he wrote for the online news site Politico this week.