On a Sunday in Washington, former and returning U.S. President Donald Trump made a sudden, consequential policy shift, directing the Pentagon to sharply curtail a planned large-scale joint military exercise with South Korea that was scheduled to kick off later that same week. The announcement tied the move to two separate developments: a claimed South Korean refusal to back U.S. efforts to denuclearize Iran, and Trump’s own long-held view that large-scale drills send an unnecessarily hostile message to North Korea.