In mid-January, a top United States materials company announced that it had started to manufacture rare earth magnets. It was important news—there are no large U.S. makers of the neodymium magnets that underpin huge and vitally important commercial and defense industries, including electric vehicles. But it created barely a ripple during a particularly loud and stormy time in U.S. trade relations.The press release, from MP Materials, was light on details. The company disclosed that it had starte...