Tusk said EU leaders would use the summit to discuss the Iran deal along with innovation, the European future for the western Balkans, and Trump's trade policies.
"Looking at the latest decisions of Trump, someone could even think: With friends like that, who needs enemies?" said Tusk to reporters.
He added: "Europe must do everything in its power to protect, in spit of today's mood, the transatlantic bond, but at the same time we must be prepared for those scenarios where we have to act on our own". While the European Union says these are two distinct issues, leaders are likely to lump both together in a wide-ranging discussion over dinner on how to respond to Trump's provocations.
The options include protecting European companies dealing with Iran from USA sanctions, allowing the European Investment Bank to invest in Iran and coordinating euro-denominated credit lines from EU states. Donald Tusk, who chairs the summits, said on Wednesday EU unity was key.
European leaders sought unity on Wednesday toward threatened USA import tariffs on steel and aluminium, balancing the views of those most fearful of a trade war and those determined not to be bullied into concessions.
European Union leaders explore ways to save Iran economic ties from United States sanctions
But Europeans are increasingly exasperated by the way Trump is steering U.S. policy, objecting not only to his stances but also to what they say is erratic policy making that switches on the whim of Fox News programmers.
"But frankly speaking, Europe should be grateful to President Trump, because thanks to him we have got rid of all illusions".
"I have no doubt that in the new global game", Tusk said, "Europe will either be one of the major players or will be a pawn".
A further issue is that the United States has agreed permanent exemptions with countries such as Brazil and South Korea, but only by imposing import quotas instead of tariffs.
Over the dinner of Bulgarian salad, meatballs, buffalo steak and walnut biscuits with berries, May meanwhile was to tell her fellow leaders that Britain was "committed to ensuring the deal is upheld" so long as Iran honours its commitments, her spokeswoman said. The letter appeared to confirm fears that pulling out of the Iran deal, which was strongly supported by European leaders like French president Emmanuel Macron, British Prime Minister Theresa May and German Chancellor Angela Merkel, could cause a rift in the relationship between the United States and long-standing allies.
They backed plans to offer concessions if the United States gives Europe a permanent exemption from the tariffs, but added that the "EU will not negotiate with a gun at its head". This decision led to clashes between Palestinians and Israeli military in the Gaza strip, during which killed 59 people, reminiscent of "Bagnet".
California governor slams Trump for 'lying' about immigration at 'sanctuary city' roundtable
Venting out his frustration at officials in both Mexico and California, Trump vowed to strengthen the US' "weak" immigration laws. Last year, multiple cities throughout the state also voted to enact sanctuary city polices in their local jurisdictions.