I can't say I'm too surprised, given "Nones" have been on the rise. It would be normal enough for those Nones to have been part of Christianity, given that's the largest religious group in the country.
Still, a bit of interesting research, as always:
US Christians numbers 'decline sharply', poll finds - BBC News
Still, a bit of interesting research, as always:
US Christians numbers 'decline sharply', poll finds - BBC News