In an attempt to protect European companies’ investments in Iran, the European Commission said it would enact regulations that would prevent those companies from complying with sanctions the U.S. will reimpose. It’s unclear how exactly this will work—European companies are already starting to withdraw investments from Iran for fear of U.S. reprisals. Iran stands to lose substantial European investment regardless, calling into question whether the Europeans can save the deal, which was premised on Iran’s getting economic benefit from accepting restrictions on its nuclear program. But ultimately the dispute says more about trans-Atlantic relations that it does about Europe’s ability to get its companies to invest in Iran.

The U.S. and Europe continue to cooperate closely on a wide range of issues, including counterterrorism and security, and a tough sanctions regime against Russia for its actions in Ukraine. They share common goals, the tariffs notwithstanding, on global trade. “Neither side wants this disagreement [over the Iran deal] to affect other parts of the relationship,” Axel Hellman, a policy fellow at the European Leadership Network, said Tuesday at a separate panel discussion at the Atlantic Council. “But … we might see foreign ministers start to question the very foundations of their relationship with Washington. Security has always been a cornerstone of that relationship, and from a security point of view this is really kicking the EU in the teeth.”

Or as Caroline Vicini, the deputy head of the EU delegation in Washington, said Wednesday at the Atlantic Council: “We’re unfortunately out of lockstep with the United States. We’re on two sides of this … very unfortunate affair.”

The debate in the U.S. over the Joint Comprehensive Plan of Action, as the nuclear deal with Iran is formally known, generally deals with the questions of whether the agreement was a good one and whether President Obama, who advocated for the accord, gave up too much to Iran in exchange for too little. But Europe sees the issue differently. European negotiators had worked toward the accord for 12 years—the U.S.’s subsequent participation starting in 2008 gave the process teeth—and saw it as the most effective way to achieve security for the continent in the face of Iran’s nuclear program.*

“There had been lots of discussions and controversies across the pond for the last decades, but this is the hardest one because we see our core national-security and continental-security interest being just ignored,” Omeed Nouripour, a German lawmaker with the Greens, told me. “This drives us into the hands of the Chinese and the Russians.”

Those two countries are also party to the JCPOA, and have signaled their intention to remain in it. But working with them presents its own challenges: Europe, like the U.S., views China as an unfair trade partner; and Russian actions in Ukraine and Syria, where it is involved on the side of President Bashar al-Assad, make Moscow an unlikely ally. Yet German Chancellor Angela Merkel has visited Russia twice in the past month—visits that prompted Russian media to ask whether a thaw in relations was imminent.