Today, as many Americans don’t affiliate with any church as belong to a major religious group. We’re talking about one of the largest religious trends, if not the largest, in the last 40 years. Ryan Burge’s new book, The Nones: Where They Came From, Who They Are, and Where They Are Going (Fortress Press), seeks to explain how these so-called “nones” grew from statistically irrelevant to around one-quarter of the entire American population.

Burge is an assistant professor of political science at Eastern Illinois University. And he’s also been a pastor in the same American Baptist church for the last 13 years. So his work goes beyond the descriptive into the prescriptive. For example, he observes that among the nones, Christians should focus on the “nothing in particular” group, which differs in many ways from atheists and agnostics by indicating openness to returning to religion.

Burge joined me on Gospelbound for a rolicking discussion of his findings and the implications for evangelicals, for Black Protestants, for the mainline, and for politics. I asked him why so many Americans left the church between 1991 and 1996 and his best guess at the most significant cause behind this trend. Listen as we debate whether the secular left or religious right, whether President Obama or his evangelical critics, is more responsible for the dramatic decline in religious affiliation.