"Looking at latest decisions of [Trump] someone could even think: with friends like that who needs enemies", wrote Donald Tusk, president of the European Council. "But frankly speaking, Europe should be grateful by President Trump. He made us realize that if you need a helping hand, you will find one at the end of your arm".
An EU source said after the dinner the 28 EU leaders agreed that, in exchange for permanent exemptions, they could discuss with Washington deeper LNG cooperation, a WTO reform and better access to each other's markets for cars and public procurement.
European officials sounded off on the Trump administration's Iran policy on Wednesday, amid signs European companies are prepared to end business dealings with the country instead of incurring possible US sanctions.
The EU is also unimpressed by Trump's decision to place tariffs on European steel and aluminium as part of his "America first" agenda.
Tusk even compared the U.S. administration to Europe's traditional foes Moscow and Beijing as he launched his broadside hours before a dinner of the 28 leaders in Sofia where they will discuss the issue.
On trade, Tusk said the US move to impose trade penalties on national-security grounds was "absurd", since the European Union is a core American ally and does not represent a threat. "This is the only real alternative".
Some European officials have also suggested the EU trigger a 1996 rule - known as the blocking regulation - which aims to limit the effect of worldwide sanctions with which the EU does not agree.
Merkel however said that Europe had no choice but to stick with the ties that have bound it to Washington since World War II.
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.
During a speech on Wednesday to the German Parliament, she also said it would be wrong to cancel the nuclear agreement with Iran and called the decision to pull out of the accord "troubling news". "This means a permanent exemption from USA tariffs on aluminium and steel if we are to discuss possible trade liberalisation with the U.S".
Trump has also broken with a key global principle of Middle East peace efforts by moving the United States embassy in Israel to Jerusalem from Tel Aviv.
Just 16 months ago, such comments would have been unimaginable coming from an European Union leader, whose continent modeled itself on the USA image in the aftermath of World War II.
Behind their message of unity and firmness, some member states seem open to tolerating limited quotas from the United States on metals imports while others want a harder line, diplomats said. This decision led to clashes between Palestinians and Israeli military in the Gaza strip, during which killed 59 people, reminiscent of "Bagnet".