On Wednesday, I texted Nick Fuentes about being the center of an existential crisis in American conservatism. Fuentes, a white-nationalist influencer, appeared on The Tucker Carlson Show in October, which has enraged a number of prominent figures on the right and set off a spiraling conversation about where to draw the line on whom the party welcomes into its mainstream. “I don’t consider myself to be hateful or prejudiced,” he told me. “Just provocative and maybe tribalistic.” Fuentes has repeatedly praised Hitler, likened “organized Jewry” to a “transnational gang,” said that women should be “subordinate” to their husband, and called...