In sharp contrast, the Pew data show, the Democratic coalition has evolved into a three-legged stool that divides almost evenly between White Christians, non-White Christians, and those from all races who identify either with a non-Christian faith or, increasingly, with no religious tradition at all. Most Americans who don’t identify with any religious faith—a rapidly growing group—now align with Democrats.

These diverging profiles create electoral challenges for each side. Republicans face the tension of balancing the morally conservative preferences of their religiously devout base with the deepening instinct toward cultural tolerance of a society that is growing more secular, particularly among the young.

Democrats must weigh the culturally liberal instincts of their now mostly secular wing of upscale Whites with the often more traditional inclinations of their African-American and Latino supporters, who are much more likely than White Democrats to identify with Christian faiths. In a landmark shift, fewer than half of White Democrats with a college degree now identify as Christians; that’s a much smaller percentage than among the party’s Blacks and Latinos.

Above all, the end of majority status for White Christians marks another milestone in America’s transformation into a kaleidoscope society with no single dominant group.

In 1944, polls showed that White Christians accounted for more than eight-in-10 American adults, notes John C. Green, an expert on religion and politics and dean of the college of arts and sciences at the University of Akron. Surveys found that number declined only slightly, to just under eight-in-10, by 1964. Even in 1984, White Christians still accounted for just under seven-in-10 American adults. The annual merge of results from other national surveys conducted by Pew, though not directly comparable with the huge Religious Landscape poll, suggest that White Christians dipped below majority status sometime between 2012 and 2013. The latest figures placing White Christians at just 46 percent of the adult population confirm a trend, Green says, in which “the relative size of White Christians [has] fallen at an increasing rate over the post-W.W. II period.”

Religion has often been a jagged line in U.S. political allegiance, but historically the key difference has been across religious faiths. The Republican Party was founded in the years just before the Civil War as the party of Northern mainline Protestants, and the party revolved around those voters well into the 1960s. Democrats functioned through most of their history as a cacophonous and often contradictory coalition of other religious traditions, particularly Northern Catholics and Southern evangelical Protestants, Green notes.

In the new alignment, those historic differences between Christian faiths have largely been sublimated to two other cleavages. In the first, Republicans now run well among the most religiously devout in all Christian traditions, while Democrats perform relatively better among Christians who are less religiously observant. In the second, while the Republican coalition still revolves around Christians, Democrats increasingly rely on Americans who identify with non-Christian faiths, or no religious tradition at all.