Kevin Roberts, the president of the Heritage Foundation, must be confused. Last month, he turned to the most reliable move in the Republican crisis-management playbook, and it didn’t work. On Oct. 30, three days after his friend Tucker Carlson released a softball interview with Nick Fuentes, a Holocaust denier and perhaps the most notorious fan of Adolf Hitler in American public life, Roberts posted a video online that decried cancel culture. “We will always defend truth,” Roberts said. “We will always defend America, and we will always defend our friends against the slander of bad actors who serve someone else’s...