Obama says: We are no longer a Christian Nation

Really?
According to the history books I read, this nation was founded by Christians who came to America to get away from religious persecution in Europe.
A Nation founded on New Testament principles.
Pilgrims, Quakers, and Puritans were Christians.
My question for Obama will be: At what point did we stopped being a Christian Nation? Can he give me the year?

My question to our Christian brothers and sisters is:
Are you ready to accept this notion without a challenge?

What say you?