Evangelical Christianity--the faith professed by one in four Americans--exerts an enormous influence in American society. Believed by some to have originated as a reaction to the social revolution of the 1960s, evangelicalism as a distinct subculture in fact dates to the advent of radio. The evangelical faithful flocked to the airwaves, developing a nationwide mass culture as listeners across denominational lines heard the same popular preachers and music. Evangelicals left behind the fundamentalism of the early 20th century as broadcast ministries laid the foundation for the culturally...