The story of how Roman Catholics “became American” is very well-known. Beginning in the 19th century, Catholics were a feared and despised immigrant population that Protestants imagined to be inimical to, even incompatible with, everything America was meant to be. American mobs burned Catholic convents and churches. By the early 20th century, the anti-Catholic Ku Klux Klan was running rampant.

But this changed after the Second World War. Military service, educational achievement, economic advancement, and suburbanization combined to make Catholics virtually …