A few weeks ago, the Democratic National Committee formally acknowledged what has been evident for quite some time: Nonreligious voters are a critical part of the party’s base. In a one-page resolution passed at its annual summer meeting, the DNC called on Democratic politicians to recognize and celebrate the contributions of nonreligious Americans, who make up one-third of Democrats. In response, Robert Jeffress, a Dallas pastor with close ties to Trump, appeared on Fox News, saying the Democrats were finally admitting they are a “godless party.”

This was hardly a new argument. Conservative Christian leaders have been repeating some version of this claim for years, and have often called on religious conservatives and Republican politicians to defend the country against a growing wave of liberal secularism. And it’s true that liberals have been leaving organized religion in high numbers over the past few decades. But blaming the Democrats, as Jeffress and others are wont to do, doesn’t capture the profound role that conservative Christian activists have played in transforming the country’s religious landscape, and the role they appear to have played in liberals’ rejection of organized religion.

Researchers haven’t found a comprehensive explanation for why the number of religiously unaffiliated Americans has increased over the past few years — the shift is too large and too complex. But a recent swell of social science research suggests that even if politics wasn’t the sole culprit, it was an important contributor. “Politics can drive whether you identify with a faith, how strongly you identify with that faith, and how religious you are,” said Michele Margolis, a political science professor at the University of Pennsylvania and the author of “From Politics to the Pews: How Partisanship and the Political Environment Shape Religious Identity.” “And some people on the left are falling away from religion because they see it as so wrapped up with Republican politics.”

Liberal Americans are less religious than they used to be

Over the course of a single generation, the country has gotten a lot less religious. As recently as the early 1990s, less than 10 percent of Americans lacked a formal religious affiliation, and liberals weren’t all that much likelier to be nonreligious than the public overall. Today, however, nearly one in four Americans are religiously unaffiliated. That includes almost 40 percent of liberals — up from 12 percent in 1990, according to the 2018 General Social Survey. The share of conservatives and moderates who have no religion, meanwhile, has risen less dramatically.

The result is that today, most people’s political ideology is more tightly tethered to their religious identity. The overlap is far from complete — there are still some secular conservatives and even more religious liberals. In fact, the majority of Democratic voters are religiously affiliated. But the more liberal you are, the less likely you are to belong to a faith; whereas if you’re conservative, you’re more likely to say you’re religious.

To be sure, religious belief and practice can still exist without a label. Many people who are religiously unaffiliated still believe in God, or slip back into the pews a few times a year. But liberals are also cutting ties with religious institutions — since 1990, the share of liberals who never attend religious services has tripled. And they’re less likely to believe in God: The percentage of liberals who say they know God exists fell from 53 percent in 1991 to 36 percent in 2018.

Politics is shaping how some liberals think about religion

At first, it wasn’t clear why so many Americans were losing their faith — and of the available explanations, politics wasn’t high on the list. After all, there are lots of reasons why any individual person would stop attending church that have nothing to do with politics. A church scandal might spark a crisis of faith. You might begin to view a religion’s hierarchies or rules as antiquated, restrictive or irrelevant to your life. You might not have been that religious to begin with.

Social scientists were initially reluctant to entertain the idea that a political backlash was somehow responsible, because it challenged long-standing assumptions about how flexible our religious identities really are. Even now, the idea that partisanship could shape something as personal and profound as our relationship with God might seem radical, or maybe even a little offensive.

But when two sociologists, Michael Hout and Claude Fischer, began to look at possible explanations for why so many Americans were suddenly becoming secular, those conventional reasons couldn’t explain why religious affiliation started to fall in the mid-1990s. Demographic and generational shifts also couldn’t fully account for why liberals and moderates were leaving in larger numbers than conservatives. In a paper published in 2002, they offered a new theory: Distaste for the Christian right’s involvement with politics was prompting some left-leaning Americans to walk away from religion.

It was a simple but compelling explanation. For one thing, the timing made sense. In the 1990s, white evangelical Protestants were becoming more politically powerful and visible within conservative politics. As white evangelical Protestants became an increasingly important constituency for the GOP, the Christian conservative political agenda — focused primarily on issues of sexual morality, including opposition to gay marriage and abortion — became an integral part of the the party’s pitch to voters, but it was still framed as part of an existential struggle to protect the country’s religious foundation from incursions by the secular left. Hout and Fischer argued that the Christian right hadn’t just roused religious voters from their political slumber — left-leaning people with weaker religious ties also started opting out of religion because they disliked Christian conservatives’ social agenda.

At the time, Hout and Fischer’s argument was mostly just a theory. But within the past few years, Margolis and several other prominent political scientists have concluded that politics is a driving factor behind the rise of the religiously unaffiliated. For one thing, several studies that followed respondents over time showed that it wasn’t that people were generally becoming more secular, and then gravitating toward liberal politics because it fit with their new religious identity. People’s political identities remained constant as their religious affiliation shifted.

Other research showed that the blend of religious activism and Republican politics likely played a significant role in increasing the number of religiously unaffiliated people. One study, for instance, found that something as simple as reading a news story about a Republican who spoke in a church could actually prompt some Democrats to say they were nonreligious. “It’s like an allergic reaction to the mixture of Republican politics and religion,” said David Campbell, a political scientist at the University of Notre Dame and one of the study’s co-authors.

Granted, the people who were leaving weren’t necessarily at the center of their religious community — they didn’t attend religious services often, perhaps dropping in once or twice a year. But the numbers began to add up, opening a rift between conservatives and liberals. According to Margolis’s research, while young people across the political spectrum tend to drift away from religion, liberals are increasingly unlikely to return.

Liberals seem likely to become increasingly secular

As a result, views about religion and its role in American society have become increasingly polarized. According to surveys by the Pew Research Center, the percentage of liberals who believe that churches and religious organizations positively contribute to society dropped from nearly half (49 percent) in 2010 to only one-third (33 percent) today. And according to 2016 data from the Voter Study Group, only 11 percent of people who are very liberal say that being Christian is at least fairly important to what it means to be American — compared to 69 percent of people who identify as very conservative.

And although the people who have left religion could return, it seems more and more unlikely. For one thing, conservative Christians are still a key part of the Republican coalition, where their agenda on issues like abortion and religious exemptions remains a high political priority within the party. This means liberals’ views of the association between conservative politics and religion could be hard to shake.

These patterns are self-reinforcing in other ways, too. Recent surveys show that secular liberals are more likely than moderates or conservatives to have spouses who aren’t religious. That’s critical because these couples are then often less likely to pray or send their children to Sunday school, and research shows that formative religious experiences as a child play a crucial role in structuring an adult’s religious beliefs and identity. It’s no coincidence then that the youngest liberals — who never lived in a political world before the Christian right — are also the most secular. “It’s very, very unlikely that a kid raised in a nonreligious liberal household would suddenly consider going to church,” Margolis said.

The political implications of this shift are already evident. As more liberals become nonreligious, the Democratic Party’s base is growing more secular, complicating the party’s efforts at reaching more religious voters. But what it means for religion is less clear. Paul Djupe, a political scientist at Denison College, said that the impact might be blunted by the fact that the people who are becoming nonreligious mostly weren’t that involved in religion to begin with.

But Campbell warned that this shift is already reducing churches’ ability to bring a diverse array of people together and break down partisan barriers. That, in his view, threatens to further undermine trust in religious groups and make our politics more and more divisive. “We have very few institutions left in the country where people who have different political views come together,” he said. “Worship was one of those — and without it, the list is smaller and smaller.”