‘I sell millions of Halloween costumes to Americans. Mr. President, here’s my takeaway from the wild tariffs ride’

For pranksters of a certain age, Fraser Smeaton is a hero. With his brother, Ali, and former roommate, Gregor Lawson, the Scottish business leader is cofounder of MorphCostumes. The U.K. company launched a twist on the zentai full-body spandex suit in 2009 and spawned a legion of viral videos. When a Gap store on Fifth Avenue was “morphed” by a band of improv-artists in 2018, the police had to be called. The accompanying video received millions of views.

MorphCostumes’ biggest market is America...