The biggest threat facing America is not a faltering economy or a spate of books by famed atheists. Rather, the country meets new challenges due to the decline of traditional Christianity, New York Times columnist Ross Douthat suggests in Bad Religion: How We Became a Nation of Heretics (Free Press). Douthat has taken his own personal tour of American Christianity: he was baptized Episcopalian, attended evangelical and Pentecostal churches as a child, and converted to Catholicism at age 17.

He argues that prosperity preachers, self-esteem gurus, and politics operating as religion contribute to the contemporary decline of America. CT spoke with Douthat about America's decline from a...