The dollar cratered on Tuesday, capping a week of steady decline that got briefly worse after Trump said a sliding dollar is “great.” The dollar has gotten weaker across the board, whether measured against a broad basket of other currencies, emerging-market, currencies, or big near-peer currencies such as the euro, against which the dollar has slid around 13 percent since Trump took office. In just the past week, Trump has also threatened new and further tariffs on Canada and South Korea—both U.S. free-trade partners—for unclear reasons. If affordability and lower interest rates were Trump’s economic goals, and they are, a weaker dollar would seem to be the wrong medicine. Surely, though, the one benefit of a cheaper dollar is that U.S. exports will be that much more competitive overseas? With a weaker dollar, all those imports will be more expensive.