...the secular posturing Obama is railing against is more a function of the party's desire to appease a powerful, but relatively small, constituency than it is a deeply held, widely shared ideological stance. Just as the Republican Party pays obeisance to the demands of the 37% of its base that is white evangelical Christian, the Democrats feel they must not offend the 22% of their core voters who claim no religious affiliation. Why not? Because although they make up less than one-quarter of the coalition, these secular Democrats are much more likely than others to be high-level party activists.
That was not always the case. Some scholars point to the Democratic National Convention of 1972 as not only the moment Democrats edged toward secularism but the event that created the religious rift in American politics. Before 1972, both major parties were essentially indistinguishable in their approach to religion. The activist cores of both were dominated by members of mainstream religious groups: the GOP by mainline Protestants and the Democratic Party by Catholics and Jews.
But the Democratic delegation that nominated South Dakota Sen. George McGovern for president at the '72 convention represented a profound shift from what had been the cultural consensus in American politics. Whereas only 5% of Americans could be considered secular in 1972, fully 24% of first-time Democratic delegates that year were self-identified agnostics, atheists or people who rarely, if ever, set foot in a house of worship. This new activist base encouraged a growing number of Democratic politicians to tone down their appeal to religious voters and to seek a higher wall separating church and state. With little regard for the traditionalist sensitivities of religious people within or outside of the party, the Democrats also embraced progressive stances on feminism and homosexuality that the public had never openly debated.
via Relapsed Catholic