Eleven days after Charlie Kirk was killed in September, Marjorie Taylor Greene, the third-term Georgia congresswoman, was watching his memorial service on TV as the luminaries of the conservative movement and the Trump administration gathered to pay tribute to the young activist. What stayed with Greene long afterward were the last two speakers who took the stage. First there was Kirk’s widow, Erika, who stood in white before the crowd filling the Arizona stadium, lifted her tear-filled eyes and said that she forgave her husband’s killer. And then there was President Trump. “He was a missionary with a noble spirit...