Last Thursday, on the same day that Trump blitzed the world, yet again, with a new round of tariffs on a broad range of goods, a specialized appeals court in Washington, D.C., inched closer to a definitive pronouncement on whether the President can legally make such sweeping economic demands—on a whim, whenever he feels like it.

The U.S. has begun officially levying higher taxes on imports from dozens of countries Thursday, four months after President Donald Trump first announced plans to impose tariffs on most of the world w