Conservatives have a problem, and it is named Nick Fuentes. An avowed white nationalist, Mr. Fuentes commands an immense following of young men he has recently been mobilizing in opposition to President Trump, who he feels has not moved far enough to the right. On Oct. 27, the influential podcaster and former TV host Tucker Carlson posted an interview with Mr. Fuentes in which he gave him over two hours to air his views, which are well outside the American mainstream, even for some of the most provocative members of the conservative movement. As some have disavowed Mr. Fuentes, a...