At this point in the primary, religiously unaffiliated Democrats seem more open to a candidate who isn’t Biden than their religious counterparts. And while there is some variation in the level of support for Biden, he’s the clear front-runner among several major religious groups. Among nonreligious Democrats, though, Biden is less of a clear favorite. Instead, a plurality (30 percent) of atheists prefer Sanders, while agnostics are split between Biden and Sanders. And although Biden is the favored candidate of 32 percent of Democrats who say they’re “nothing in particular,” nearly one-quarter support Sanders. Meanwhile, Sen. Elizabeth Warren is also somewhat more popular among atheists and agnostics than she is among other religious groups.

The most obvious explanation for the split among religious and nonreligious voters is that religiously unaffiliated Democrats — in particular, atheists and agnostics, who together accounted for 17 percent of primary voters in the 2016 CCES study — are substantially more liberal than Democrats who are still part of organized religion. And very liberal voters are a key constituency for Sanders. “Many religiously unaffiliated voters overlap with the liberal wing of the Democratic Party, so it’s not surprising you’d see higher support for Sanders,” said Ryan Burge, a political science professor at Eastern Illinois University. Religiously unaffiliated Democrats also tend to be younger overall — another group in which Sanders tends to be strong relative to Biden.