The “crisis of evangelicalism” that arose in 2016 with the election of Donald Trump, who was supported by 80 percent of American evangelicals, provides a case study in the challenge of determining who counts as a “true evangelical” or a “true Christian.” The distinction between descriptive and prescriptive approaches to Christianity helps to clarify much of the controversy. The anxieties of modernity have forced all Christians, liberal and conservative, to explore new approaches to prescriptivism.