Thomas Paine famously complained that the ¡°unwritten¡± constitution of Britain was no constitution at all. Rules governing matters such as who was entitled to govern the country and under what conditions were eminently the sort of thing that had to be written into law, fixed and made visible. Events in the US over the past two years make me wonder whether he was right. Having sided with Paine all my life, I find the idea that he was wrong disturbing.

Although the US Constitution is a very compact document, written in simple prose - unlike the 2,450 pages of the Patient Protection and Affordable Care Act or ¡°Obamacare¡± - few Americans really know what is in it. Jill Lepore¡¯s engaging collection of essays, The Story of America, retells the absurd tale of what happened in 1987 when respondents were asked whether various familiar phrases appeared in the Constitution; 82 per cent thought that ¡°government of the people, by the people, for the people¡± was part of the Constitution (rather than the Gettysburg Address), and 45 per cent thought ¡°from each according to his ability, to each according to his need¡± was in the Constitution (rather than Karl Marx¡¯s Critique of the Gotha Programme). Eighty per cent thought ¡°all men are created equal¡± was there, too; but that is more forgivable. Anyone might think that the Declaration of Independence was a prologue to the Constitution.

Less amusingly, the national tendency to confuse the Constitution (which was expected by its creators to need pretty continuous updating as their new nation changed and grew) with the Bible (whose Author would not look to His creatures for revision and amendment) has become a disaster. It would under any circumstances be difficult to persuade the American public that the Constitution was littered with absurdities - two senators per state, giving North Dakota as much clout in the Senate as California? - but it has become utterly impossible to alter, now that half the population is convinced that anything it dislikes - the Affordable Care Act, for instance, or bans on gay marriage - must be unconstitutional.

It would be less absurd if the Supreme Court were not such an obstacle to modest reform. The dominance of money in political campaigns is the most striking feature of American politics. Less striking - until political scientists ferret out the details - is how this carries over into the making of public policy; on some estimates, the least well-off 80 per cent of the population exercises no influence on the policies that emerge from Congress, or to put it another way, if they agree with the best-off 20 per cent, they get what they want, and if not, not. Liberals are conflicted, since they would like the poor to have a larger share of the national cake but don¡¯t relish the views of the less prosperous on abortion, gay marriage and school prayer becoming the law of the land.

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Ever since the Supreme Court decided in 2010 that corporations were ¡°persons¡± in a strong enough sense to be entitled under the First Amendment to the free speech rights of flesh-and-blood people, American politics has been awash in the money of right-wing ideologues such as the Koch brothers and Sheldon Adelson - the elderly casino billionaire who pledged $100 million (?62 million) to defeat President Obama. He failed of course, but it meant that the president had to spend time raising nearly $1 billion to fend off his well-heeled adversaries.

Still, even that absurdity pales into insignificance alongside the Supreme Court¡¯s rulings on the Second Amendment - the one that guarantees Americans the right to bear arms. Since local politicians are, if anything, dottier than the Supreme Court, it means that anyone teaching at the University of Colorado-Boulder can expect to start next autumn with their students carrying concealed weapons. The Second Amendment originates - like much in the Constitution - in the misbehaviour of British monarchs and their ministers, in this case James II¡¯s attempt to return Britain to the Catholic fold with the help of Louis XIV. He hoped to ensure that local militias, especially in London, could not present organised resistance to a French invasion. Sacking Protestant officers and installing Catholics in their place would do the trick. William III had to agree that the king would not prevent ¡°those of his subjects that are Protestants¡± from serving in the militia. The pledge was one of the terms on which he became king.

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It is easy to see how you might get from that to the Second Amendment; it was an extension or elaboration of the Constitution¡¯s prohibition on requiring religious tests for office. Nobody could impose a religious test for joining a militia. Contrary to popular imaginings, the founders were meticulous about keeping God out of the creation of their new nation; He got on to the currency only in 1864 during the Civil War, 77 years after the Constitution was created; He got on to the pledge of allegiance only during the Cold War.

It is harder to see how to get from there to the widespread view that anyone not visibly deranged or too incompetent to hide a criminal record is entitled to purchase weapons ranging from handbag-sized revolvers to automatic rifles whose only purpose is to kill lots of people on a battlefield - or, as it might be, in a shopping mall, cinema or infants¡¯ school. Even without the Second Amendment, it would be hard to cure Americans of their taste for large-scale mayhem; and the American unwillingness to understand that the US is not ¡°exceptional¡±, but just one more complicated modern industrial society, will not be overcome in a year or even a decade. Still, if the roadblock of the Constitution and its interpreters on the Supreme Court were removed, common sense might prevail: sooner rather than later. But on current projections, never.