trade wars are good, and easy to win

Last invoked in 1996 and causing the US to withdraw its threat of imposing secondary sanctions on Cuba, the European Union has adopted a blocking statue that provides a measure of protection to member state corporations that continue doing business with Iran and license to ignore the hectoring bluster emanating from the White House.
Though continued trade could be frustrated in practise, EU companies that are negatively impacted by the US unilateral departure from the terms of the deal with Iran and restoration of punitive tariffs can seek recovery through the courts and refuse to recognise jurisdictions that enforce the sanctions, which are backed only by the US (making good on a pandering promise made to mobilised, useful idiots) and few regional powers that stand benefit from a weaker Iran.