Mr Tusk said: "Besides 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".
In a striking rhetorical assault on the leader of Europe's biggest ally, EU Council President Donald Tusk said, given Trump's recent decisions, "someone could even think 'with friends like that, who needs enemies?'". "But frankly speaking, Europe should be grateful to President Trump, because thanks to him we have got rid of all illusions". He has made us realize that if you need a helping hand, you will find one at the end of your arm.
"My objective is simple - we stick to our guns", Tusk said of the expected leaders' discussion on trade. Trump has also broken with a key global principle of Middle East peace efforts by moving the US embassy in Israel to Jerusalem from Tel Aviv.
But the EU's hopes have been complicated by the fact that European companies would also be exposed to United States sanctions imposed on anyone doing business in Iran.
The options being discussed include new credit lines for Iran, increased energy cooperation and the use of EU laws to block European companies from caving in to USA sanctions.
With Trump's cabinet being increasingly populated by the likes of National Security Adviser John Bolton and Secretary of State Mike Pompeo, who have long pushed for regime change in Iran, the U.S. position is becoming more at odds with those of Europe, Russia, and China.
Trade tensions have been growing since March 23, when Donald Trump ordered to introduce a 25% tariff on steel imports and 10% tax on aluminum, claiming to protect the U.S. producers from unfair competition and boost national security. Therefore U.S. tariffs can not be justified on the basis of national security.
Tusk's comments came ahead of a gathering of heads-of-state of the European Union in the Bulgarian capital Sofia on Wednesday.
That came a day after many European newspapers featured dueling photographs on their front pages: the beaming visage of first daughter Ivanka Trump opening the new U.S. Embassy in Jerusalem, and the smoky carnage an hour's drive away in Gaza, where scores of Palestinian protesters were killed by the Israeli military. And Mr. Trump's decisions to recognize Jerusalem as Israel's capital and to move the United States Embassy to the holy city were made despite European opposition.
"We notably discussed concrete practical solutions to make sure the European Union can continue to live up to its commitments under the deal and protect our economic operations", said Avramopoulos, the EU's migration commissioner.