Last month, Tucker Carlson, the host of one of the country’s most popular podcasts, interviewed Nick Fuentes, a white-nationalist influencer, for more than two hours. The two men got along famously, and it was little wonder why. Carlson has become a fierce and obsessive critic of Israel; he has interviewed a Holocaust revisionist and said that “Christian Zionists” have “been seized by this brain virus.” Not everyone on the right was pleased. So in the aftermath of the Carlson-Fuentes conversation, Kevin Roberts, president of the Heritage Foundation, put out a video defending Carlson, a “close friend” of the institution, against...