Donald Trump’s trade war has been an abstraction for most Americans so far, but the retaliation has now begun in earnest and the casualties are starting to mount. The President’s beloved stock market took another header Monday on news of more restrictions on investment into the U.S., and the Dow Jones Industrial Average is now down for 2018. But the biggest losers Monday were the American workers who make Harley-Davidson motorcycles whose jobs will soon be headed overseas thanks to the Trump tariffs.

***

Last year Mr. Trump...