Agree that it's part of the white supremacy iceberg that still exists. I can't fault Egan for not connecting the dots between the Klan and, say, the Proud Boys--he's writing history, not political science--but the links are so clear, a part of me wishes he had.
Some people argue that the Klan has morphed into today's white supremacist groups: that neo-Nazis and other groups replaced it when it became unacceptable to march in parades in white pointed hoods. It's a plausible argument that such groups, instead of being a "new," were here all along under another name. Thanks for bringing that connection into sharper focus in this space.