On average last year, 36 percent of Americans in ABC News/Washington Post polls identified themselves as members of a Protestant faith, extending a gradual trend down from 50 percent in 2003. That includes an 8-point drop in the number of evangelical white Protestants, an important political group.

Reflecting the change among Protestants, the share of Christians overall has declined from 83 percent of the adult population in 2003 to 72 percent on average last year. In the same time, the number of Americans who say they have no religion has nearly doubled, to 21 percent.

Catholic self-identification (22 percent) has held steady during this time.