The primary religious concern of our Founding Fathers was that no state religion be established in America and that no political entity have the power to impose religious beliefs on individuals.
Those who now claim the U.S. is a "Christian nation" seem to be satisfied that any reference to "God" by the Founding Fathers proves that we are indeed a "Christian" nation. The fact that neither the Constitution nor the Declaration of Independence makes reference to Christ or Christianity puts a damper on their insistence.
Most historians readily concede that the framers of the U.S. government (Washington, Jefferson, Franklin, Madison, Paine) were not Christians, but Deists. They believed in an uninvolved Creator who may have fashioned the universe, but who certainly had no power over or interest in the lives of the individual citizens.
All these men did, indeed, mention "God," but none of them, except John Adams, professed a Christian belief. Washington, for example, refused a Christian burial.
Jefferson rewrote the New Testament, removing all references to miracles because he trusted in reason, not faith. Even the American Christian Heritage blog admits that Franklin "became a prominent Deist."
John Adams, who admittedly was the most Christian of the Founding Fathers in his private life, signed the 1797 Treaty of Peace and Friendship, unanimously ratified by the Senate. This treaty stated, "The Government of the United States of America is not in any sense founded on the Christian religion ..."
What is most evident is that the Founding Fathers saw a clear difference between their private religious beliefs and public policy.
We would do our country a greater service by focusing on the tolerance advocated by the Constitution instead of attacking the beliefs of those who disagree with us.