Schaffner’s data shows an even larger religious gap among white college graduates. This group is less religious than whites without degrees — 36 percent answered “very important,” 22 percent “somewhat important,” 15 percent “not too important” and 27 percent “not at all important.”

The 2018 House Democratic vote among white college graduates for whom religion is not at all important was 91 percent; for those who said religion is very important, 30 percent voted Democratic, a 61 point gap.

The less religious, Schaffner wrote told me “are more likely to be male (57 percent), and are much younger (average age of 44, compared to average age of 52 among those for whom religion is important).” In addition, the nonreligious are much less likely to be married, tend to live in urban areas and are more likely to be found in the Northeast and West than other regions.

In his book “Red Fighting Blue,” David Hopkins, a political scientist at Boston College, pointed out that:

voters’ religious affiliations and degrees of religiosity now exert considerable influence over their partisan identification and choice of candidates; the Pew Research Center found in 2015 that white evangelical Protestants had come to prefer the Republican Party by a margin of 68 percent to 22 percent, while religiously unaffiliated voters now leaned toward the Democrats by 61 percent to 25 percent — a 40-point gap that equals the magnitude of the more longstanding difference in the partisan preferences of whites and African Americans.

While cultural liberals and cultural conservatives are not truly at “war,” Hopkins continued, “they are increasingly lining up on opposite sides in the ongoing electoral competition between the two major parties.”

The steady growth in recent years in the number of people who respond to the question “what is your religious preference” by saying they have “no religion” has clearly benefited the Democratic Party, which now depends on the nonreligious for nearly three out of every 10 votes it gets.

By 2018, according to Burge’s analysis, these voters had become the largest religious category, 28 percent, of the Democratic electorate, outnumbering once dominant Catholics at 21.8 percent, evangelicals at 14.1 percent, black Protestants at 12.9 percent and mainline white Protestants at 14.4 percent.

Three political scientists — David Campbell and Geoffrey C. Layman, both of Notre Dame, and John Green of the University of Akron — have developed a multidimensional analysis of religiosity in their forthcoming book, “Secular Surge: A New Fault Line in American Politics.”