While the formal separation of church and state is a vital element of America's constitutional order, the success of our long-running experiment in self-government has always depended on a healthy interdependence between republican freedom and religious faith. So argues Jonathan Rauch in his new book Cross Purposes: Christianity's Broken Bargain with Democracy. "In American civic life, Christianity is a load-bearing wall," writes. "When it buckles, all the institutions around it come under stress, and some of them buckle, too."

On this episode of The Permanent Problem podcast, Rauch joins host Brink Lindsey to discuss secularization and the rapid decline of organized Christianity in recent decades -- in Rauch's words, the combination of "thin Christianity" in the mainline denominations and increasingly "sharp Christianity" among self-described evangelicals. They examine the underlying causes of these developments, how they stoke polarization and undermine democratic values and institutions, and what a healthier "thick Christianity" might look like.