“Mr. President, what do you think about the U.K. getting into business with China? Keir Starmer is in Beijing,” the reporter asked at the premiere of a documentary about the president’s wife Melania. “It’s very dangerous for them to do that,” Trump began, before quickly pivoting to Canada, against whom he has long held a grudge. The president was particularly unhappy after Prime Minister Mark Carney met his Chinese counterpart in Beijing and announced a landmark “new strategic partnership” aimed at reversing years of strained relations. “Canada’s not doing well; they are doing very poorly, and you can‘t look at...