In 2012 we witnessed a collapse in American evangelicalism. The old religious right largely failed to affect the Republican primaries, much less the presidential election. Last month, Americans voted in favor of same-sex marriage in four states, while Florida voters rejected an amendment to restrict abortion.

Much has been said about conservative Christians and their need to retool politically. But that is a smaller story, riding on the back of a larger reality: Evangelicalism as we knew it in the 20th century is disintegrating. ...