In 1990, we were eight percent of the population; today we’re 15 percent and climbing. The good news? We’re taking over. The bad news? It’s, er, not quite clear who “we” are.

American religious nones tend to be religious skeptics as opposed to outright atheists. Fewer than ten percent of those identifying with no religious tradition call themselves atheists or hold atheistic beliefs, according to the new study.

“American nones are kind of agnostic and deistic, so it’s a very American kind of skepticism,” says Barry Kosmin, director of Trinity’s Institute for the Study of Secularism in Society and Culture. “It’s a kind of religious indifference that’s not hostile to religion the way they are in France. Franklin and Jefferson would have recognized these people.”

Only seven percent of the non-religious are atheist — versus 27 percent who believe in a “personal god”? Dude, weak:

What kind of “non-religious” person believes in a personal god, anyway? This kind, I guess.

There are, of course, political implications here:

Secular voters once constituted an important part of the GOP coalition, but fewer than 10 percent of religious nones under age 30 are Republican. “Republican nones are getting older and continue to show an affinity to the GOP,” says Juhen Navarro-Rivera, a Trinity College research fellow who helped compile the new report. “But they’re not making new Republican nones.”

Navarro-Rivera is still running the numbers, but his hunch is that the new generation of religious nones has been scared away from the Republican Party because of its ties to the Christian right. Does the GOP continue to embrace that movement or move more to the middle? Call it the Sarah Palin option versus the John McCain option. (Though opposition to healthcare reform, it should be noted, is helping bring the two camps together.)

Here’s a graphic breakdown of the partisan split. Note how much wider the gap is among “nones” since 1990: From a 27/21 Democratic advantage to 34/13 now.

No surprise either to find that “nones” are already at or above 20 percent on the west coast and in the northeast, where the GOP’s collapsed over the past 10 years:

As fascinating and portentous as all this is, the only issue I can think of where religious affiliation might strongly drive the partisan reaction is teaching evolution in schools. Behold:

That’s a staggering divide, with a majority among all U.S. adults saying evolution probably or definitely didn’t happen versus a huge majority among “nones” saying that it probably or definitely did. Exit question: Imagine an America 100 years from now that’s majority non-religious. Imagine it.