Is Christianity ceasing to matter in the US? The question might seem absurd in the light of statistics that show a country which still publicly respects religion to an extent difficult for a European to imagine. Fewer than a third of all Americans admit that they seldom or never go to church. There is only one member of Congress who claims to have no religion, and every single congressional Republican identifies as a Christian except for two Orthodox Jews. But there are good reasons to suppose that these figures are misleading, and the role of Christianity as part of the social and political convulsions of the country today is changing and diminishing in important ways.

Traditional American Christianity was shaped by British experience in the 17th and 18th centuries: it was Protestant, patriotic, and providential, but not much concerned with doctrine. The rejection of any religious establishment opened the way for competition between individual churches and then produced the extraordinary organisational and theological creativity that distinguished the US from all previous Christian societies. America seemed to some observers to provide the unquestioned future of religion in a globalised world. There was, and is, a church for every possible niche, from Unitarian Universalists to the Westboro Baptists.

The price of this exuberance was doctrinal incoherence. If there is a Christianity for everyone, Christianity can mean almost anything, and this has effects that ripple out far beyond believers. A religion that is responsive to the pressures of the market will end up profoundly fractured, with each denomination finding most hateful to God the sins that least tempt its members, while those sins that are most popular become redefined and even sanctified. In the end, a market-driven religion gives rise to a market-driven approach to truth, and this development ultimately eviscerated conservative Christianity in the US and left it the possession of hypocrites and hucksters.

There were churches on both sides of the civil war, and churches on both sides of the civil rights struggle. Martin Luther King observed that America was never more segregated than on a Sunday morning. These racial divisions carried over and even deepened in the culture wars of recent decades. White evangelical churches defined themselves against a coastal elite. The strategy was electorally successful for decades, but at a high price. It is absolutely clear from the presidential election results that white evangelical Protestants voted overwhelmingly for Donald Trump, but they could not deliver the popular vote. The Catholic church in the US is increasingly Hispanic. Pope Francis has come close to declaring that Mr Trump is not a Christian at all – a Christian should build bridges, and not walls, he said last year.

Meanwhile, the close identification of evangelical Christianity with the Republican party, and with the rejection of evolution, climate science and sexual equality, has repelled young people and may have accelerated a long trend of decline between generations that looks inexorable. More than a third of Americans under 50 now say they have no religion. Some even call themselves atheists, long the most distrusted minority in the US, who now outnumber Mormons. Change is going to come.