The Protestant mainline, by whatever name, was bound to make a comeback—at least as a subject of academic discourse.
The “mainline” is usually identified with seven Protestant denominations, it was always a small group, and shortly after it acquired its name, it began to shrink. After the shrinking began, journalists lost interest in liberal Protestantism, except to retell the story of mainline decline, and the academy lost interest in it, except to sneer that “liberal religion” is oxymoronic and no match for the fundamentalist Right.
Now, as the New York Times recently noted, the books on liberal Protestantism and liberal religion are coming fast. Some are about the overlooked legacy of liberal Protestantism and some are about varieties of liberal religion in the United States.
David Hollinger, After Cloven Tongues of Fire: Protestant Liberalism in Modern American History
Matthew Hedstrom, The Rise of Liberal Religion: Book Culture and American Spirituality in the Twentieth Century
Elisha Coffman, The Christian Century and the Rise of the Protestant Mainline.