Donald Trump’s tariffs are a headache for all his trade partners. But the U.S. president’s plan to impose ad hoc “reciprocal” levies on imports are a particular problem for the European Union. By enabling him to target whichever countries in the bloc he pleases,

Hoping to head off a potential trade conflict, a top European Union official stressed the importance of active engagement and fairness in trade during a four-hour meeting with Trump administration officials.

Commission President Ursula von der Leyen said unjustified tariffs would prompt "proportionate and decisive countermeasures", echoing her vow on Tuesday of a "firm and proportionate" response to Trump's decision to impose tariffs on all steel and aluminum imports.