For most of the country’s history, white Christian America—the cultural and political edifice built primarily by white Protestant Christians—set the tone for our national conversations and shaped American ideals. But today, many white Christian Americans feel profoundly anxious as their numbers and influence are waning. The two primary branches of their family tree, white mainline and white evangelical Protestants, offer competing narratives about their decline. White mainline Protestants blame evangelical Protestants for turning off the younger generation with their anti-gay rhetoric and tendency to conflate Christianity with conservative, nationalist politics. White evangelical Protestants, on the other hand, blame mainline Protestants for undermining Christianity because of their willingness to sell out traditional beliefs to accommodate contemporary culture. [emphasis added]
The key question is not why one white Protestant subgroup is faring worse than another, but why white Protestantism as a whole—arguably the most powerful cultural force in the history of the United States—has faded. The answer is, in part, a matter of powerful demographic changes.
Rod Dreher had a comment soon enough, and he's eloquent enough to let his words speak for themselves here:
The problem with this is assuming that “white Christian America,” as defined by demographic data, is the same thing as the Christian faith as held by all white people. It’s not. Me, I don’t care that the religious influence of white Christians is declining. I care that the influence of orthodox Christianity is declining. [emphasis original]
I know white Christians who profess views that I find antithetical to small-o orthodox Christianity, and Arabs, Asians, and African-Americans who hold to a faith I recognize as authentically Christian. I prefer to stand every single time with non-white Christians who stand for the Gospel than with Christians of my own race and cultural tribe who do not.
My own take is that the mainline represented what you could call the Social Gospel of the old Religious Left, while the evangelicals, at least since Reagan, came to be known as the Religious Right. Both are so morally and intellectually bankrupt at this point it's hard to see either as tragic victims of the influence of the other. They sold themselves out to power and empire-building in different ways but they both did it. Both sides seem to have sold out to a pragmatic socio-political realpolitik that is just blue-state or red-state American civic religion.
The decline of the influence of the WASP doesn't necessarily mean that religion is going away from the American public sphere. Jacques Ellul's rather grim proposal was that politics itself would become the new religious commitment stand-in for people in industrial societies that avail themselves of the tools of propaganda.
What may continue to happen is that the WASPs of the left and right may continue to imagine they get to define the discourse for the rest of global Christianity. Episcopalians who are in the United States or Canada may conclude that they get to tell the entirety of the Anglican presence in Africa how things are going to go ... and ... the irony of this would be it would still be a kind of white colonialist superiority complex, that. Now, sure, the Religious Right is only in the last generation or so hip to the irony of that ... but that might just be because it was convenient to notice.
Cranky white radicals and reactionaries have had their pet candidates this year, Sanders and Trump, but it remains to be seen whether angry whites on the left and right who think they should be making the case for who should have the executive office are going to be the deciding vote this year.
It's hard to take either seriously at the moment, but then I concede that I'm a fatalist and a pessimist about politics. The right wants to revive the imagined glory days of American empire and the left wants to bankroll what's left of it into a more generous welfare state ... but the welfare programs of the past could work in part because of the wartime profit and production on the one hand, and on the other hand, as plenty of people have been able to point out, that social safety net, to the extent that it worked, seemed pretty racist in its outworkings. So there's a sense in which WASPs on the left and right are both ultimately nostalgic for an empire whose golden era is past, whether the empire of the United States itself or their conception of their respective roles within it.