If he wins, it must mean only one of two things: either he has succeeded in cheating at the election by stymying mail voting and undermining the election's legitimacy, or the American people have genuinely re-elected him despite his dangerously erratic foreign-policy forays; his destructive trade policies; his employment of toadies and cronies and his supplicancy to autocrats and dictators. Indeed, they would have endorsed those actions. Either way, the US would be neither a worthwhile ally nor a worthy one.

Indeed, the US's NATO partners should also go it alone for the same reasons.

Many initially thought after the 2016 election that US institutions, administration officials and advisers would sandpaper down the worse elements of Trump. It was not to be. The leopard's spots could not be changed.

I hope Trump does not win and do not think he will, but never underestimate his capacity to cheat and to pander to the base instincts and resentments of enough people.

The failure of the Senate to throw Trump out of office after the impeachment just made him more brazen. Imagine how much more brazen he would become if - by hook or by crook - he got back.

The test this election is of Lincolnian proportions: the survival of government by the people, of the people and for the people. It is a test for the US Constitution. Will the checks and balances sewn into the Constitution 232 years ago stop the tide of tyranny?

There are some good signs. His appointments to the Supreme Court have applied the rule of law against Trump's side in some key litigation. It surprised Trump who thought they were "his" judges.

Some key people associated with the Republican Party, notably George W. Bush's Secretary of State Colin Powell and former Ohio Governor John Kasich, have backed Joe Biden - putting country above party.

Congressional inquiries have made Trump's life at least a little uncomfortable and the states have pushed back somewhat.

But the danger remains. Many in the US remain concerned Trump will sabotage or steal the election.

When the rise of Trump is put into global context, the importance of the US Constitution and its institutions (which Trump has done his damnedest to undermine) becomes obvious.

The world is seeing a new sort of authoritarianism. It is of a quite different degree from the totalitarianism of Communism and Nazism. It is almost impossible for that sort of totalitarianism, in which every aspect of life is controlled by the party, to survive in today's internet world.

But the authoritarian tendencies remain similar, and they can be seen in Trump's behaviour over the past four years, as they can be seen in populist-authoritarian leaders is many other countries: Russia, Poland, Turkey, Hungary, the Philippines and any number of Middle Eastern, African and former Soviet republics - countries which liberal democrats had hoped after 1990 would have become rule-of-law democracies.

A major tendency is to make loyalty supreme in selecting officials. (Remember Trump's unrequited demand for personal loyalty from FBI director James Comey). So is resentment of elites, merit and competition. Loyalist cronies and family members are given key jobs, enabling them to enrich themselves.

The new authoritarians practise what historian Anne Applebaum in Twilight of Democracy calls "restorative nostalgia". They want their nation to return to an earlier era when things were better - in Trump's case "to Make American Great Again".

The new authoritarians allow an opposition; elections; and freedom of speech and assembly, but only so far as they do not threaten their grip on power.

They champion nationhood not as a set of ideals, abstractions and institutions, but a cohesive unit of "us" - in Trump's case, white Christians, especially gun-owning males. They are intolerant of diversity, complexity, nuanced rational argument and expert advice. They have simplistic solutions. They belittle and humiliate anyone who dares challenge them.

They oppose international co-operation and free trade.

They undermine - with the aim of destroying - independent media; the judiciary; a professional civil service; and free and fair electoral processes, as Trump is doing now through the donor and supporter he appointed to head the US Postal Service in order to undermine postal voting.

The recent rise of social media in the past seven years or so is the common element to the rise of the populist, nationalist autocrats. Just as the rise of printing 500 years ago upended power structures giving rise to first religious wars and then the enlightenment, the rise of social media is creating similar upheaval.

In a way it is similar to the rise of the new medium of radio in the 1930s which was seized upon by ultra-nationalists in nations which did not set up independent government-owned broadcasting services or guarantee diversity of broadcasting outlets as in the US.

Trump has used social media to send political opponents and those standing up for the rule of law, safety and environmental standards, minorities and diversity into a frenzy. With every narcissistic rant or mad policy proposal his opponents have to expend large amounts of time and effort hosing the ideas down only to find another one emerges almost immediately. He exhausts them.

Trump has gone nowhere near as far as leaders in Poland, Hungary and the Philippines, but his grip on power is now threatened.

The battle for America in November is not between the Republican and Democratic parties, nor between right and left, or capital and labour, or even rich and poor.

Rather it is a fight for the ideals of the US constitution against a man who would happily destroy them in pursuit of his own power and self-image by exploiting fear, hatred and resentment.

So just as a number of American Republican Party friends of US democracy have come out against Trump because he threatens that democracy, so to should friends of US democracy abroad.

Australia, New Zealand and the members of NATO should note that in the past four years Trump's destructive actions undermining alliances and allies while praising authoritarians have not abated. They would only get worse if he is re-elected. If he is, they should suspend the alliances until true American democracy is restored.