A responsible American president would pull America’s friends back from this brink. For all the anguish, Brexit still has not happened yet. Britain has filed formal notice of its intention to leap off the precipice, but its feet as yet still touch the ground. The EU authorities have accepted the notice, but paperwork does sometimes get postponed, revised, lost, or forgotten. By now, the U.K. and EU alike would likely welcome a face-saving compromise—one that spares the U.K. the humiliation of asking to be released from the exit process it triggered, one that protects the EU from the disruption of losing its most economically dynamic and militarily capable member state. The EU’s own rules offer no obvious off-ramp from the looming crunch—but American help and American pressure might possibly construct such an off-ramp just in time.

Maybe the solution is postponement followed by a second British referendum on the choice between the new renegotiated deal and the pre-2016 EU status quo.

To date, though, America has played no role, raised no voice. Trump has repeatedly welcomed Brexit. His national-security adviser has long advocated it. The rest of the administration is too paralyzed and dysfunctional to remonstrate against the president’s malign indifference, much less reverse it.