One senior U.S. State Department official said Trump's foreign policy closely hews to Republican thinking in Washington and that tensions had been high for some time.
The official added that despite the current strains, the administration "deeply values this relationship."
"These are our closest allies and we really appreciate their support. There has been this tension, which has been a long-running factor ... but I'm pretty positive on the relationship overall," the State Department official said.
Trump's May 8 decision to pull out of Iran accord was a severe setback that has led to talk among EU officials of an "existential moment" in European diplomacy.
They say it also shows that EU efforts to develop a relationship with the White House, including high-profile visits by the French President Emmanuel Macron and German Chancellor Angela Merkel, have largely failed.
That leaves the EU seeking other alliances, including closer ties with Japan and help from Moscow and Beijing to keep money connected to the nuclear deal flowing to Tehran.
"We used to roll our eyes at Trump's policies but now we are seeing the craziness becoming strategic," another senior EU diplomat who was at the Hill meeting said. "We now have to seek out all kinds of partners to further our goals."
