Mr. Hovater, 29, is a welder by trade. He is not a star among the resurgent radical American right so much as a committed foot soldier — an organizer, an occasional podcast guest on a website called Radio Aryan, and a self-described “social media villain,” although, in person, his Midwestern manners would please anyone’s mother. In 2015, he helped start the Traditionalist Worker Party, one of the extreme right-wing groups that marched in Charlottesville, Va., in August, and again at a “White Lives Matter” rally last month in Tennessee. The group’s stated mission is to “fight for the interests of White Americans.’’