In a ruling heard ’round the world, the U.S. Court of International Trade on Wednesday blocked President Trump’s sweeping tariffs. This is an important moment for the rule of law as much as for the economy, proving again that America doesn’t have a king who can rule by decree. The Trump tariffs have created enormous costs and uncertainty, but now we know they’re illegal. As the three-judge panel explains in its detailed 52-page ruling, the President exceeded his emergency powers and bypassed discrete tariff authorities delegated to him by Congress. The ruling erases his April 2 tariffs as well as...