Whether Donald Trump wins or loses in 2016, this much is certain: Trumpmania will be studied for decades to come.

Many people will ask: Who's to blame? My answer: All of us.

But though we are all culpable in Trump's rise, I'd like to focus on one aspect of the Trump phenomenon that is often underrated: religion.

There's a puzzle in Trump's success at the polls. He's winning self-described evangelical voters. And yet, Christians who attend church regularly are overwhelmingly anti-Trump. Part of the explanation is that there's never been a clear definition of what an "evangelical" is. By its nature, evangelicalism is a decentralized phenomenon, and evangelicals proudly don't have an institutional church, let alone a pope or a magisterium. Someone who "gave his life to Jesus" at a summer camp when he was 15 but doesn't go to church and doesn't read the Bible can still call himself "evangelical" to a pollster.

But that's only part of the answer. To understand the religious aspect of the rise of Trump, you have to understand the changing landscape of American religion. To do that, there is probably no better book today than Bad Religion: How We Became a Nation of Heretics, by New York Times columnist Ross Douthat.

Douthat's starting point is to note that the debates among the elites about the direction of religion in America miss the point of how religion is actually lived by the vast majority of Americans. Most debates in the intelligentsia focus on whether American culture is going to stay soaked in the old-time Christian religion, or whether it will secularize in the way of Western Europe. But most Americans are nowhere in those two extremes.

More Americans than ever report having a personal relationship with God or having had spiritual experiences. At the same time, church attendance is down. And if you ask Americans about their beliefs, what you find isn't either orthodox Roman Catholicism or rock-ribbed Calvinism, but a hodge-podge of beliefs, still clearly connected to historical Christianity in many ways, but also different in significant ways. In other words, as Douthat writes, America is a nation of heretics.

And heresy is the right word. The Christian gospel has always sought to hold together a synthesis of seemingly contradictory ideas. The early Christians argued about whether Jesus was human or divine. He is, somehow, both, Christian orthodoxy maintains. Heresy comes in when people try to make sense of the seeming contradiction by removing one side of the equation, and take it to an extreme. So some Christians argued that Jesus was only human, and others argued that Jesus was only divine. And so on down the line of Christian history.

America has always been a land of religious iconoclasts, experimenters, and innovators, Douthat notes. The difference today is that traditional organized religion provided a counterweight to that innovation. Each kept the other in check and helped to enrich the other, providing a sort of religious balance.

But since the 1950s, institutional religion has gone into decline. The Protestant Mainline, once almost an unofficial American state church, is terminally ill (the average age of Episcopalians is in the mid-sixties). The Catholic Church is mired in scandal. And evangelicalism, so vital, is distinguished precisely by its decentralization, and has hit a ceiling in American society because of a not-completely-unjustified perception of its politicization. The decline of institutional religion has ceded the field to heresy.

What are those heresies? Well, two that Douthat identifies sound tailor-made for Trump.

The first is Christian nationalism. This is an old heresy in American life, now mostly found on the right, that believes, in a sense, that America is a new "chosen people" or a New Israel. Obviously, religion and nationalism together form a combustible mix. Here, the heresy of Christian nationalism takes a Christian idea — that nations and political bodies have a role to play in God's unfolding design — and takes it to the extreme of divinely ordered nationalism, forgetting the counterbalancing idea of the Christian gospel that all humans are brothers and sisters in Christ.

It's easy to see how the heresy of Christian nationalism could power the rise of Trump. If you're a Christian who believes so deeply in American exceptionalism that you forget that, actually, God judges all nations, and that all fall short of the glory of God, you might see in Trump's overt nationalism a quite natural thing, and be ready to brush off his other departures from what is usually considered good Christian conduct, such as his bigotry, his cruelty, or his misogyny.

The other major heresy is the prosperity gospel. In its most crude forms, the prosperity gospel says that God rewards financially those who pray. If you don't have the car you want or the house you want, if you pray hard enough, God will give it to you. Again, this takes the very biblical idea that God sometimes rewards the righteous in this life, while forgetting the equally biblical idea that sometimes the righteous have to suffer, and sometimes they have to expect their reward in the afterlife — and that a man's worth is never, ever judged by his possessions.

The prosperity gospel is one of the most vibrant heresies in America today, one that is frequently overlooked by the commentariat, given that it preys mostly on the poor and the uneducated. But one of America's most powerful religious leaders is undoubtedly Joel Osteen, who is a prosperity preacher. It's obvious why someone taken in by the prosperity gospel would see no glaring contradiction between Trump's assertion that he's a "very strong Christian" and his gaudy lifestyle and ostentatious wealth.

In fact, if you're aware of the profound hold that such heresies have on many people, Trump looks less like an aberration than the incarnation of those heresies. Trump looks like the incarnation of a presidential candidate for a formerly Christian culture that sometimes likes to think of itself as Christian, but worships money and power instead of Jesus.