President Trump’s threat to withdraw from the Iranian nuclear deal could spell the immediate return of crippling U.S. secondary sanctions, which had largely cut off Iran from the global economy between mid-2010 and late 2013. A potential re-imposition of U.S. secondary sanctions would again force foreign persons, including individuals, businesses, and other public and private entities all over the world, to choose between the U.S. and the Iranian market. Under such a likely scenario, that could materialize as soon as mid-May, the European Union would find itself in a highly difficult position. Despite its ironclad support for the Iranian nuclear deal, it currently lacks the tools to effectively prevent major European companies from abandoning the Iranian market.

This is primarily because commercial interests of European businesses in the U.S. market outweigh the relatively modest penalties for breaching an existing EU regulation that, if updated by the European Council, could legally prohibit EU persons from complying with re-imposed U.S. secondary sanctions.

How could EU policy-makers respond to a U.S. withdrawal from the Iranian nuclear deal short of initiating a major transatlantic trade war? How did European governments respond to the extraterritorial application of U.S. primary and secondary sanctions in the past and what are the key lessons for contemporary transatlantic relations?