Europe and the Trump administration fundamentally differ on "what is a good, acceptable resolution" of the dispute, according to Forrer. Secretary of State Mike Pompeo's speech this week, in which he said he now relies on Iran is making more nuclear-related concessions, but is overbearing his foreign policy, ceasing ballistic missile testing and releasing US citizens in captivity.
"What Pompeo articulates is very different than what the EU would articulate," Forrer said. "Where does it end?"
The ultimate impact of the rift could be difficult to measure, according to Forrer.
European leaders did not hide their frustration at a summit in Bulgaria last week following the U.S. exit.
"I think the real geopolitical problem is when you have an unpredictable opponent or enemy or partner," said European Council President Donald Tusk. This is the essence of our problem today with our friends on the other side of the Atlantic. "