A Voice from the Past - Lewis

Thus the 'decline of religion' becomes a very ambiguous phenomenon. One way of putting the truth would be that the religion which has declined was not Christianity. It was a vague Theism with a strong and virile ethical code, which, far from standing over against the 'World', was absorbed into the whole fabric of English institutions and sentiment and therefore demanded church-going as (at best) a part of loyalty and good manners as (at worst) a proof of respectability.

C. S. Lewis, 1898-1963, God in the Dock, Part II, 8 The Decline of Religion (Wm. B. Eerdmans Publishing, 1970, pp. 219-220)

Is the decline of religion in the United States of the same character? How should that affect our approach to it?