During the Biden administration, conservative challengers won Supreme Court victories that limited the president’s power to craft policy in matters from student-debt relief to air pollution. Now, those precedents are returning to haunt one of their greatest champions: President Trump. On Wednesday, a specialized federal court in New York invalidated the worldwide tariffs Trump imposed to address a range of issues on his agenda, from international trade imbalances to cross-border trafficking of fentanyl. The unanimous decision by the U.S. Court of International Trade relied in part on the “major questions” doctrine, which the Supreme Court adopted in 2022 to bar...