"Looking at the latest decisions of President Trump, someone could even think with friends like that who needs enemies", Tusk told reporters.
It is further said to be forming a united European front against the USA in response to leaving the Iran nuclear deal and imposition of trade tariffs on Europe. Trump's decision to pull out of the Paris climate change accord and the 2015 nuclear deal with Iran threaten Europe's own foreign policy, which was long complementary to Washington's.
After listing more of their proposals, Nigel finished: "So the whole European project is crumbling, the third biggest country in the eurozone is in open revolt against the whole system and all Donald Tusk can do is say a few sad words about Donald Trump".
According to the source, they reaffirmed that they will "not negotiate with a gun at its head", but they said they are ready to talk with the United States once its decides on a permanent tariffs exemption for the EU.
"Besides the traditional political challenges such as the rise of China or the aggressive stance of Russian Federation, we are witnessing today a new phenomenon: the capricious assertiveness of the American administration", Tusk said.
"Frankly speaking, Europe should be grateful to President Trump because, thanks to him, we have got rid of all illusions".
"I would like our debate to reconfirm without any doubt that as long as Iran respects the provisions of the deal, the European Union will also respect it", Tusk said. "This is the only real alternative". "He made us realize that if you need a helping hand, you will find one at the end of your arm".More news: Scotland refuses to green light Brexit bill, setting up constitutional clash
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"Europe must do everything in its power to protect, despite today's mood, the transatlantic bond. But at the same time we must be prepared for those scenarios, where we will have to act on our own", he added.
On Iran, the leaders expressed backing for a plan including "EU support for JCPoA, as long as Iran respects the deal", the source said, referring to the deal's formal name, the Joint Comprehensive Plan of Action.
"The broader US-EU security relationship is at risk", a former US envoy to the EU, Anthony Gardner, told the European Parliament on Wednesday.
Tusk said he wanted the European leaders to "reconfirm" that they will stay in the Iran deal, as long as Tehran respects it - although Europe must now find a way to make up for the U.S. sanctions on Iran that Trump will reactivate.
It was crucial, he said, that the European Union stuck to its guns and refused to talk trade with the United States until it received a permanent exemption from punitive tariffs on steel and aluminium imposed by Washington on the grounds of national security.
Tusk demanded a permanent exemption from the threatened tariffs for the European Union, and said any claim by the USA that such tariffs are justified for national security would be "absurd".
"The EU will continue fighting for a rules-based global system despite recent decisions on climate change, tariffs and Iran", the source said after the leaders met over dinner in Sofia.