Over the past 40 years, Americans have become increasingly likely to deny an affiliation with a religion. The graph below shows that people with “no religious preference” rose from about 5% of the population in 1972 to about 20% today. Overall, however, Americans do not report a corresponding decline in the a belief in God, life after death, or other religious ideas. What’s going on?

Sociologists Michael Hout and Claude Fischer — the guys who made the graph above — argue that the retreat from religious affiliation is essentially, a retreat from the political right. Religion has become strongly associated with conservative politics, so left-leaning people are choosing, instead, to identify as “spiritual but not religious.”

Here is some of their evidence. The data below represents the likelihood of rejecting a religious affiliation according to one’s political views. The more politically liberal one is, the more likely they have come to reject religion.

Using fancy statistical analyses, they explain: “generational differences in belief add nothing to explaining the cohort differences in affiliation.” That is, people haven’t lost their faith, they just disagree with religious leaders and institutions. Hout and Fischer conclude:

Once the American public began connecting organized religion to the conservative political agenda — a connection that Republican politicians, abortion activists, and religious leaders all encouraged — many political liberals and moderates who seldom or never attended services quit expressing a religious preference when survey interviewers asked about it.

Democrats have wondered how to break the association of the right with religion and claim a little bit of moral authority for themselves. It looks like they may not need to or, even, that having failed to do so has a surprise advantage.