There is an old adage about boiling a frog. It used to be said that if you put a frog in extremely hot water it would jump straight out, whereas a frog deposited in cold water gradually heated on the stove to boiling point would stay put throughout. The poor creature adjusts to the change in temperature until it is too late. Cue dead frog.

That concept, the notion of a gradual adjustment to what was once deemed unthinkable, comes to mind when one considers the state of the US election. Is contemporary America the equivalent of the poor frog being boiled? Will it jump out just in time before boiling point is reached? Or on Tuesday will American voters elect Donald Trump to be their next President and then realise too late what happened?

So completely and utterly bonkers has this campaign been that even reasonable people have by now been rendered unshockable. The madness has raged for such a long time that many Americans – and friends of America – have become immunised to further outrage. It is not simply that Trump’s ludicrous lies are so frequent and commonplace that they no longer attract much comment or attention. There were 27 Trump untruths in just one day’s campaigning on the stump last week, it was recorded.

That is bad enough, but Trump’s rambling rhetoric is simply an exaggerated post-modern version of the old carnival huckster populist prepared to say anything to fool people. Much more troubling in this contest has been the corrosion of basic democratic norms.

It should be thought quite incredible, a subject of urgent legal investigation, that a foreign power and its surrogates have already had considerable success in disrupting the election. Huge caches of secret documents and communications have been dumped, and reported for months as though they are all accurate and untampered with. This provides the backdrop for endless rumours – transmitted by parts of what the US commentator David Frum terms the Conservative Entertainment Complex – that serve to suggest that because the emails show Clinton in a bad light then America, or the West more broadly, is inherently corrupt.

One irony here is that many of the liberals who cheered on disgraceful outlets such as WikiLeaks a few years ago, when they undermined our security, are now horrified at where the spiral of anti-Western spying and condemnation of the US has led. It has led to Russia, very efficiently and with clinical ruthlessness, working behind the scenes for a pro-Putin Trump victory. Well done everyone.

Of course, the Democrat candidate Hillary Clinton has mishandled the email scandal, displaying once again her own strange relationship with the truth. But her indiscretions and failings on this are trifling by the standards of non-democracies or dictatorships.

Where Trump’s approach has done most damage is in terms of democratic legitimacy. He has accelerated the development of a trend favoured by America’s two parties in recent decades. That is the refusal to accept defeat or the legitimacy of rivals when they win, as happened in 2000 with Bush v Gore and earlier in Bill Clinton’s travails. Trump the spoilt man-child has taken it to caricature levels in declaring before the election that he will only accept the result if he wins.

This is perfect for Putin. Trump and his surrogates even help the Kremlin make its key point. The Russian message (echoed by China) is that Western liberal democracy is a sham, a decadent carnival of idiocy and no proper way to run things. The hacking and targeted leaks are designed to push this bogus idea that it is all a pointless, corrupt farce, rather than an imperfect but noble and essential means for maintaining a free society, on which all else rests. Tens of millions of Americans are attracted to Trump’s strong-man schtick and now doubt that democracy is trustworthy or even desirable.

It is standard to say that this outpouring of nativist populist anger, in favour of Trump and against the elites, is at root about economics and the failure of wages and opportunities to keep up with expectations since globalisation and the financial crisis. There is much more to it than that.

A clash of cultures is partly responsible, between white, gun-carrying, pro-hunting, had-it-with-political-correctness Americans, and millions of their opposites. The old ideological left-right dividing lines don’t much apply either. Many Trump supporters want their social welfare entitlements and big government programmes.

But something else is at play too, that echoes the experience in Britain during the Scottish Independence and Brexit referendums. It is not enough for us to disagree with each other or for our opponents to be wrong. They must be stupid and their motives bad. We do it on both sides of all these arguments, when on a subject such as Brexit the situation rather obviously requires a degree of compromise and coalition-building to find a way forward.

In the US I suspect it has much to do with deep changes in the media. American friends cite as a contributory cause the carnage that has hit the newspaper industry, and the closure and destruction of many local and city newspapers. This is where communities traditionally got their news about local politics, business, good works, bad deeds and sports. Those disappeared or diminished American newspapers were far from flawless, but they did provide a civilised space in which basic facts were accepted even if there was disagreement on what might be done in response.

The rise of political talk radio, and that Conservative Entertainment Complex, helped cut listeners off from alternative points of views and inconvenient facts. The radical left has its equivalent in online publications and the documentary format pushing an angry agenda.

That process has been supercharged by social media, where consumers and voters can live untroubled by hearing that they may be wrong. Facebook or Twitter when used for politics become echo chambers, where we seek out the like-minded and denounce opponents. This militates against complexity, ambiguity, acceptance of difference and civility.

This deterioration means that it will be difficult to build broad movements, and to create a healthier politics where the outcome is respected. In the US, the Republicans in particular will have to work out how they might regenerate themselves and create a new, mainstream, economically liberal, patriotic, aspirational, sensible, welcoming, appealing party. All that must come after next week’s excitements, for which I’ll be in New York.

It turns out, incidentally, that the boiling a frog adage is completely wrong. Scientists ran the experiment years ago and the frog put in a pan of boiling water jumps out (or dies from shock). The frog put in cold water jumps out too when the temperature is turned up and rises to an intolerable level. The frog, the experts say, tends to get the message.

Time to jump out, America.