President Trump is escalating his trade rhetoric, threatening China and Europe with more tariffs on more goods if they don’t agree to his terms. Mr. Trump says winning these trade wars is “easy,” so let's take a look at the early returns on his steel and aluminum tariffs and the retaliation they’ve inspired.

Commerce Secretary Wilbur Ross in March slapped a 10% tariff on aluminum and 25% on steel in the name of helping American metal manufacturers. But one problem is that downstream businesses can’t easily reconfigure global...