When will the U.S. lose its Christian majority?

[Starbucks Union Thug HokeyPuck]

Within 100 years, I believe that the majority of the population of the United States will either declare to be agnostic, or in essence be agnostic.... as many people already are.  (those people who through family or going strictly by holidays they observe might identify themselves with a certain religion... but when honestly asked about God, the afterlife, etc., give the very agnostic answer of "I really don't know").