President Donald Trump’s 25% tariffs on steel and aluminum imports came into force Wednesday, triggering an immediate reprisal from the European Union as the global trade war enters a new and perilous phase.

Trump previously said he would increase from 25% to 50% tariffs for Canada after Ontario said it would raise electricity prices on U.S.

U.S. tariffs on Canada have put experts at odds over how appropriate the action was, particularly given the unaddressed demand side of the fentanyl epidemic.