Just before his election to serve as New York City’s next mayor, Bill de Blasio addressed his religious affiliation in response to rumors claiming he was an “anti-church” atheist. De Blasio responded by saying that while he’s not affiliated with any particular congregation, he is a spiritual guy. Making the distinction between being an atheist and identifying as religiously unaffiliated may seem minor, but the difference between the two is surprisingly significant in the minds of many Americans.

On a “feeling thermometer,” a scale that runs from 1 to 100 where 1 indicates very cool feelings and 100 indicates very warm feelings, Americans overall report significantly cooler feelings toward atheists (43) than toward those who simply identify as non-religious (56). Similarly, a survey conducted earlier this year found that about 4-in-10 (39 percent) of Americans believe atheists are changing the country for the worse, while fewer (31 percent) say the same thing about non-religious people. But does this evident discomfort with atheists affect voting decisions? PRRI’s own 2011 American Values Survey found two-thirds (67 percent) of the public reported that they would feel uncomfortable with an atheist serving as president. And a June 2012 Gallup poll found that when asked whether they would vote for a generally well-qualified person from their own party for president if that person happened to be an atheist, just 54 percent of the public said yes, while more than 4-in-10 (43 percent) reported that they would not. (This may help to explain why there’s no sitting member of Congress who identifies as atheist, and just one who says she’s religiously unaffiliated.)

The growth of the religiously unaffiliated, who now account for roughly 1-in-5 Americans, may presage warmer feelings toward atheists. Yet what seems more likely, at least in the short term, is that views of the non-religious will improve. Few Americans who are religiously unaffiliated actually identify as atheist. Among the unaffiliated, 3-in-10 (30 percent) are unattached believers, nearly 4-in-10 (38 percent) are seculars, while roughly one-third (31 percent) are atheist or agnostic.