Rarely has an economic policy been repudiated as soundly, and as quickly, as President Trump’s Liberation Day tariffs—and by Mr. Trump’s own hand. Witness the agreement Monday morning to scale back his punitive tariffs on China—his second major retreat in less than a week. This is a win for economic reality, and for American prosperity. Make that a partial win for reality. The Administration agreed to scrap most of the 145% tariff Mr. Trump imposed on Chinese goods on April 2 and later. What remains is his new 10% global base-line tariff, plus the separate 20% levy putatively tied to...