That isn't so, PEW gives the American population as 51.3% Protestant, and 23.9% Catholic, making up a total of the 75.2% of the 78.4% Christian total.
Mormons, Jehovah's Witnesses, and the Orthodox making up the odd percent.
That’s my POINT! They identify themselves as non-Catholic Christian, but NOT as a particular denomination (or as non-denominationalist). And they don’t belong to a church. See the Yearbook of the National Council of Churches; the 25% I cite is the sum of all denominations PLUS the total who claim to be non-denominationalist.
“Total church membership reported in the 2011 Yearbook is 145,838,339 members, down 1.05 percent over 2010.”
“1. The Catholic Church, 68,503,456 members, up .57 percent. “
That leaves 77 million non-Catholic Christian church members. Minus 4 million Orthodox, that leaves 73 million. Out of 290 million people 5+ years old, that’s 23% Catholic and 25% Protestant. And about 60-70 million “Christians” who belong to no church.