Tusk told a news conference in Sofia, Bulgaria, on Wednesday that “Europe should be grateful” to Trump since he has "rid Europe of all illusions" with the trade dispute and withdrawal from the Iran nuclear agreement, officially known as the Joint Comprehensive Plan of Action (JCPOA).
Tusk said the EU had to be united to face "a new phenomenon - the capricious assertiveness of the American administration."
"Looking at the latest decisions of President Trump, someone could even think that with friends like this, who needs enemies?" Tusk said.
He said the EU needed a united front on the Iran nuclear deal, noting, “We must maintain it."
Tusk said that the EU needed to protect European companies against US decisions.
Trump announced on May 8 that Washington was walking away from the JCPOA, which was reached between Iran and the five permanent members of the UN Security Council -- the US, Britain, France, Russia and China -- plus Germany in 2015.
Trump also said he would reinstate US sanctions on Iran lifted by the accord and impose "the highest level" of economic bans on the Islamic Republic.
The deal lifted sanctions in 2016 in return for Tehran limiting its nuclear program.
The remarks come as in their first meeting since the US withdrawal from the JCPOA, EU leaders were expected to meet to explore options on Wednesday for keeping the Iran nuclear deal alive and protecting their reviving economic cooperation with Tehran.
The head of the European Commission, the bloc’s executive, Jean-Claude Juncker, will also present options to shield European investments in Iran and the reviving economic cooperation.
The options include protecting European companies dealing with Iran from US sanctions, allowing the European Investment Bank to invest in Iran and coordinating euro-denominated credit lines from EU states.
Iran has reiterated it would remain in the JCPOA for now, pending negotiations with the other signatories in the coming weeks before making a final decision on its future role in the agreement.
Iranian Foreign Minister Mohammad Javad Zarif met EU foreign policy chief Federica Mogherini and his counterparts from Britain, France and Germany in Brussels on Tuesday and tasked their experts to come up with measures for a meeting of their deputies in Vienna next week.
