"The question is how aggressive the US are going to be in implementing the sanctions"
While the US pulls out, the EU holds its position. Member states say they'll be sticking to the Iran nuclear deal - but could they have done more to avoid the current turmoil?
"It's not that they didn't do enough. It seems to be a very profound decision by the US president based on his say analysis and his views. so it's little to do what the Europeans have tried," said Cornelius Adebahr, from Carnegie Europe.
But the US sanctions won't come back immediately - it will be months for the energy ones, while they'll be a 90-day winding up for everything else.
So could this buy the EU some time?
Adebahr commented: "The question is how aggressive are US going to be in implementing the sanctions. These sanctions they didn't come to force today or tomorrow it will take the number of weeks and months for the sanctions architecture to be back in place, and that provides a window of opportunity for the Europeans to also engage with the Americans to what extent it is possible to maintain this European involvement in the deal."
The question is whether Iran will want to stick with the deal.
Its supreme leader already casting doubt, saying there was no trust in the EU countries sticking with it.
"Domestic pressure in Iran will mount, President Rouhani has more or less tide himself to the deal, also in his re-election campaign, so if the deal will to actually die and were to be torn up then he has little to show for and his hardline opponents will make that clear and they will say we've always distrusted the Americans. Now we see we're proven right."