Donald Trump Jr. was perfectly at home. It was day three of the annual Conservative Political Action Conference, commonly known as CPAC, and hundreds of activists had piled into a ballroom to hear the president’s elder son speak via live-stream. He was slated to have a conversation at Liberty University with the school’s president, Jerry Falwell Jr., though it was unclear, exactly, what that conversation would be about. While most other CPAC speakers were constrained by specific topics, such as “Protecting the Freedom of Jerusalem” and “Deficit Hawks: An Endangered Species?,” Don Jr.’s appearance was headlined on the agenda as...