America is not a Christian nation, as the religious right and many Republicans would have it, intended by its founders to be governed by Christian principles or, more radically, biblical law. That's because of our constitution, but also because throughout its complex history in America, Christianity has never been a monolith, but rather subject to the uniquely American religious imagination – and uniquely American political intrusions and manipulations.

Mainline Protestant churches, believed by the conventional wisdom to be in decline, were, in the last half of the 20th century, subject to persistent attack by organised, well-funded political opposition intended to undermine their religious credibility – and their political clout, both nationally and in their communities. So, for example, when the Episcopal church was attacked by schismatic conservatives over the ordination of gay and lesbian priests, it appeared to outsiders that the conflict was about sexuality and theology. That's what got the blood boiling in the pews – but in the end, legal fights were over who controlled the land and the churches that sat on them.

The maligning of do-gooder Protestants is far older than Glenn Beck's assault on social justice. Self-anointed defenders of the faith in the early half of the century cheered union busting and opposed the New Deal; during the cold war demagogues like the Reverend Billy James Hargis attacked the liberal National Council of Churches as a treasonous, anti-American cabal infiltrated by God-hating communists.

More American presidents, though, have been Episcopalians than any other denomination. Before conservative activists went after mainline churches over sexuality issues, Episcopalianism was the denomination of prestige, of white-shoed power and pre-eminence in the community. Travel to any town in America, ones ravaged by economic despair, with downtown shop fronts boarded up or replaced with usurious cheque-cashing outfits and dollar stores, and still, the most majestic building in town can be the Episcopalian church. But more congregants probably pack the cinderblock start-up nondenominational outfit on the outskirts of town.

That, too, comes from a uniquely American tradition: the storefront church, the great equaliser, the engine of a class-blind clergy, where self-taught preachers who said they had a calling garnered followers as easily as the seminary-educated man. The 20th century saw the explosion of Pentecostalism, too, capturing imaginations with the 1906 Azusa Street revival in Los Angeles. Since that moment over a century ago, different strands and movements evolved, with some, such as the Word of Faith, or prosperity gospel, drawing on 19th century New Thought movements, and decidedly unorthodox quasi-theology that emphasised the power of positive thinking.

Mormonism, a made-in-the-USA iteration of Christianity, isn't "strange" – or, at least, isn't any more "strange" than other religions or other quintessentially American interpretations of Christianity. Many critics of Mormonism would just as quickly condemn the emergent church movement or LGBT-inclusive churches, or, for that matter, Muslims.

While countless Christians shelter undocumented immigrants in their churches and otherwise work to advance the rights of the poor and dispossessed, money and power can catapult a "Christian" to the foreground of popular culture. The politicised church, which has submerged religion under politics but claims to be the only real keeper of the flame, feeds off attention from vote-hungry politicians. Their pastors become players on the national stage, even while subject to criticism from their orthodox brethren and secularists alike.

Rick Warren's "purpose-driven" theology, for example, is considered unbiblical by some Christian critics. Kenneth Copeland, whose Word of Faith doctrine is considered heretical by Christians from both conservative and liberal traditions, is nonetheless quietly courted by Republican presidents and presidential hopefuls. He believes Jesus wants him to fly on a $20 million private jet while he sponges money off his television viewers.

The governor of Texas, Rick Perry, who plans to run for president, hosted a prayer rally that featured believers in signs, wonders, prophecies and spiritual warfare inspired by Joel 2. These are the generals Perry hopes will lead an army of believers, who insist that America must repent for the "sins" of abortion and homosexuality, to propel him to greater heights of political power. The candidate to whom he presents the greatest challenge, Michele Bachmann, studied law not how most American attorneys learn it, but through a curriculum designed by Christian Reconstructionists, who aim to have America governed by "biblical law".

What happened to American Christianity? It is constantly reimagined, manipulated and exploited. It has filled people with joy; it has filled people with piety, both true and false. It has filled people with disgust. It has filled people with rage. It has been politicised. It has been monetised. It became more inclusive for some, but anachronistic for others. And once again, a particular version– one rejected by a great many Christians – is centre stage for the presidential campaign season.