Open Culture has an article on the popularity of religious groups in the United States. The growth of those declaring “no religion” over the last couple of decades is noteworthy.
The reasons given are also interesting. A non-belief in God is only the fourth most popular reason; complaints about religious institutions scores higher. Much of the decline seems to have come from “mainline” protestant denominations.
These changes have significant political effects:
“Evangelicals punch way above their weight,” says [Ryan] Burge. “They turn out a bunch at the ballot box. That’s largely a function of the fact that they’re white and they’re old” … A 2016 PRRI report noted that “religiously unaffiliated Americans do not vote in the same percentages as evangelicals, and are often underrepresented at the polls … Additionally, and most importantly to point out any time these numbers come up: “the nones” is an entirely overdetermined category full of people who agree on little.”
That compares problematically with the evangelicals who tend to vote a lot and as a bloc.