Over the last decade the American presidency has passed from a man who arrived at his Inaugural shaking his fist in the air like a tinpot dictator to one who carelessly inserts dangerously impulsive remarks into crucial diplomatic speeches. What on earth is going on here?

Of course, the United States, like all mass democracies, has had some pretty poor leaders over the centuries. Those figures who embodied the great moments in its history – Jefferson, Lincoln, Franklin Roosevelt – are memorable because they are rare. But what is happening now seems like something more than a routine spell of mediocrity which will pass with the coming of a new generation.

What is wrong with the presidency seems more closely connected to what is happening in the wider society: nothing less than a collapse of the political culture which affects the daily lives of ordinary people in ways that failures of the federal power structures rarely have.

It is important to understand that throughout much of the country’s history, the complexion and competence of the government in Washington had relatively little bearing on the everyday quality of local American life. The quite explicit design of the Constitution guaranteeing states’ rights ensured this. It was the clear intention of the Founding Fathers to limit the central authority of Washington which was seen as a threat to the self-determination of citizens almost on a par with colonial rule. The explosive confrontations between federal and state authority over the abolition of slavery and, a century later, the enforcement of racial integration, were the most vivid examples of this but disputes over abortion and gun laws still revolve around that basic principle, built into the nation’s idea of itself, of state autonomy.

Very rarely, in fact, has the quality and tenor of the presidency seemed so closely aligned with the state of the nation in ways which can be felt in the streets and the homes of real people. The demoralisation and paralysis in Washington plays out in everyday experience. There is endless news coverage of crime, racial violence and civil disorder on a scale that many Americans believed until quite recently was behind them, as well as the continued decline of what would once have been thriving industrial enterprise. But much more ubiquitous and bewildering is the sense that the idea of an American mission – the country’s original idea of itself – has disintegrated. The collapse of that self-belief, of the accepted understanding of what America was for, is stunning.

But, you may ask, what is so different and dangerous about this? After all, identity crises of a similar kind have occurred in many countries – particularly former imperial powers which have had to come to terms with their role in a changed world order. There can be a temporary nervous breakdown and then a recovery which reframes a country’s goals. Why shouldn’t this formula which appeared to work in so many European countries apply in the United States with its famously enterprising and adaptable population? Because America is different. I would venture to say that it is much more different from any Old World society than most Europeans appreciate. In the sentimental twentieth century, there was understood to be an American Dream which animated the hopes and aspirations of those millions who arrived there in search of safety, freedom and economic opportunity. The real truth is that America itself was a dream: its national identity, and the patriotism which was a mandatory part of it, was a beautiful fiction created by a small group of people and sanctified by a handful of superb documents which enshrined the 18th century idea of liberty under the law.

Most pertinently, this new entity was intended to bind all incomers from anywhere in the world into a cohesive society which was prepared to accommodate anyone who would sign up to the social contract that was on offer. (This is precisely how the Constitution is taught to American schoolchildren: as a contract between the government and the people.) This was an unprecedented political project. Not even the original French revolution which based itself on a similar Enlightenment foundation had done anything like this: attempted to invent an entirely new nation composed of disparate, displaced people which would somehow cohere into a proud unified sense of statehood and individual belonging. And miraculously, for the longest time it worked. The patriotic rituals which most Europeans found faintly absurd, if not positively sinister, like the pledge of allegiance to the flag which began every school day, served their purpose. The children of immigrants, many of whom, like my grandparents, spoke only the language of the Old Country, went to school and learnt – like my father – to speak English. They became proud Americans who wanted more than anything to belong to this new thing that they felt a part of and were told that their commitment had helped to create.

True, there was a constant tension between loyalty to the American national identity and the sense of one’s family roots. So there were communities of Italian-Americans and Polish-Americans and Irish-Americans (like Joe Biden) who never forgot where they came from even though anything that hinted at a lack of full-hearted commitment to America was a kind of blasphemy. But even that uneasy settlement is finished now. The contractual agreement that Americans were one people with one sense of purpose, has been smashed to pieces by wilful divisiveness: identity politics which sees historic injustice as unforgivable and life choices as creating irreconcilable differences, have blown apart that fragile accord.

The people who abandoned their inherited identities in order to take part in this extraordinary, brave project are now faced with the consequences of rootlessness. Without the resources that go with generations of life in a recognisable place they are lost. Maybe the great American experiment has finally failed.