OPINION: Tariffs, Mr. Trump’s Miracle Cure

So we’re going to tax Americans until Mexico stops allowing people from Central America to exercise their legal right to seek admission to the United States?

Seems pretty foolproof.

President Trump announced Thursday evening on Twitter, his preferred medium for policymaking, that he plans to impose new tariffs on all imports from Mexico, “until the illegal immigration problem is remedied.”

The tariff would begin at 5 percent on June 10 and gradually rise to 25 percent by October.

Mr. Trump persists in the falsehood that tariffs are paid by America’s...