This decline is the latest chapter in a story dating to the 1960s. The trends unleashed in that era — not only the sexual revolution, but also consumerism and materialism, multiculturalism and relativism — threw all of American Christianity into crisis, and ushered in decades of debate over how to keep the nation’s churches relevant and vital. …

But if conservative Christianity has often been compromised, liberal Christianity has simply collapsed. Practically every denomination — Methodist, Lutheran, Presbyterian — that has tried to adapt itself to contemporary liberal values has seen an Episcopal-style plunge in church attendance. Within the Catholic Church, too, the most progressive-minded religious orders have often failed to generate the vocations necessary to sustain themselves.

Both religious and secular liberals have been loath to recognize this crisis. Leaders of liberal churches have alternated between a Monty Python-esque “it’s just a flesh wound!” bravado and a weird self-righteousness about their looming extinction. (In a 2005 interview, the Episcopal Church’s presiding bishop explained that her communion’s members valued “the stewardship of the earth” too highly to reproduce themselves.)