Is the American era officially over?

A “rupture” in the world order. That declaration last week from Canadian Prime Minister Mark Carney was more than a criticism of President Donald Trump’s recent elbow-throwing on the global stage. To many observers, it was a eulogy for the age of American preeminence.

The world is “witnessing the self-immolation of a superpower” via Trump’s trade wars and territorial aggressiveness, said Garrett M. Graff at Wired. “The old order is not coming back,” Carney declared in Switzerland. That speech...