A deepening transatlantic rift as "flattery" fails to sway Donald Trump has left Europeans in search of new answers, including closer dealings with Russia that only recently would have been unpalatable, analysts say.
The US president's decision to ignore European pleas to save the Iran nuclear deal is the latest humiliation after his threats to impose trade tariffs, his pull-out from the Paris climate pact, and his demands for NATO allies to pay more.
Analysts and officials say Trump threatens to create all by himself the kind of split between allies that Russia and China have tried and failed to foster for years, with Europe now relying on Moscow and Beijing to keep the Iran deal alive.
Trump is "uncontrollable" and "won't listen to anyone", an EU official who met the president when he visited Brussels in May 2017 told AFP.
German Chancellor Angela Merkel warned this week that Europe could no longer rely on the United States to "protect" it, while French President Emmanuel Macron said that "we cannot let others decide for us."
Both leaders made humiliating pilgrimages to Washington to beg Trump to stick with the Iran deal, only to see him withdraw -- and on the eve of "Europe Day", a public holiday for the EU institutions.
Apart from the impact on international security, European firms stand to be badly hit when Trump reimposes sanctions on Iran's nuclear programme which had been suspended under the deal.
Former US ambassador to the EU Anthony Gardner tweeted that Trump's Iran pull-out "made the world a far more dangerous place" and scathingly remarked: "So much for European efforts at flattery."
European leaders will discuss the Iran deal and trade at a summit next week in Bulgaria where EU President Donald Tusk said Trump would "meet a united European approach."
The Europeans now faced a "critical and historic choice" over how to react to the Iran deal in particular, said Ellie Geranmayeh, expert at European Council on Foreign Relations.
"The Europeans now need to essentially have a very hard and aggressive negotiating posture with the US," Geranmayeh told AFP
"The accommodation and compromise attitude by the E3 over the past few months to reach a deal with the US has basically failed," she said referring to Britain, France and Germany, the three EU signatories to the Iran deal.
That could increasingly see Europe propelled closer to Russia in particular, in spite of deep tensions over the Ukraine conflict, Syria, and the recent poisoning of a Russian ex-spy in Britain.
"The US withdrawal from the deal could benefit Russia," Moscow-based geopolitical expert Alexey Malashenko told AFP.
"Russia could profit by getting closer to the EU and saying 'look, we are still in agreement on some issues, we agree on this subject, against the United States."
Many in Europe see the Trump rift as a chance to finally leave America's orbit and increase EU cooperation on defence and the economy
The EU is keen to boost integration as it reboots itself after the shock of Brexit -- the British vote to leave the bloc fed by the same wave of populism that fuelled Trump's rise to power.
A strong proponent of this is European Commission chief Jean-Claude Juncker, who said that relations between the EU and the United States were in "crisis".
"Washington no longer wants to cooperate with the rest of the world and we are at the stage where we have to replace the United States," Juncker said in a speech in Belgium earlier this week.
While the Iran deal fiasco has created tensions, "the damage may be the greatest" from the looming transatlantic trade war over Trump's decision to impose damaging tariffs on European steel and aluminium, former ambassador Gardner warned.
But the decades of close cooperation across the Atlantic since World War II will prove difficult to abandon entirely.
"We focus a lot on areas like climate change, attitudes to Iran, where there are clearly very big differences," Malcolm Chalmers, deputy director-general of the RUSI military think tank in London, told AFP.
"But there are lots of other issues, not least in relation to Russia still, where fundamentally the positions are the same."
Chalmers added that it was "one of the ironies of Brexit" that Britain was now, less than a year before its departure from the EU, closer to its European allies on foreign policy issues than it was to the United States than it had been for some time.