In the months leading to the infamous 2017 Unite the Right Tiki-torch rally in Charlottesville, Virginia, then-talk radio host Dave Reilly had some messaging-strategy tips for the attendees from the alt-right, the internet-savvy collection of racist and antisemitic groups that arose during the Trump era. Using the screen name Davy Crockett, Reilly was part of a private invitation-only online group involved with brainstorming, planning and promoting the rally, courtroom testimony and leaked chat messages subsequently revealed. He chided members for posting a Nazi meme publicly on Facebook where the left could use it against them. He advised alt-right gays to...