Image copyright Joe Raedle Image caption Las Vegas prepares for the final presidential debate

Las Vegas was the home of "fear and loathing", Hunter S Thompson wrote more than 40 years ago in the novel that he described as a savage journey to the heart of the American dream. He'd be laughing again now.

There is, no doubt, a possibility that in the debate in Sin City on Wednesday Donald Trump will swivel and face the other way, putting the angry rhetoric of recent speeches behind him. But no one thinks it likely.

The reason is obvious. He has defined himself by his style. Without it, he'd seem a candidate with little to say.

But it has drawn him inexorably to the place where senior Republicans - Speaker Paul Ryan and Senator John McCain chief among them - always feared he would end up.

He rails against them, against the media, even against the authorities who supervise the election, and talks mainly to those Trumpeteers whom he has no need to convert.

As for the others - a majority of the electorate - he gives the impression that he suspects them of letting him down. Can't they see that he's being pursued by an establishment out to get him? So his anger rises.

Apocalyptic tone

Hillary Clinton scheduled no public rallies in the days leading up to this debate - a deliberate decision to let Trump have the stage to himself, in the expectation that he would choose the path of more confrontation and opt for an apocalyptic tone encompassing equal quantities of rage and hurt. He has obliged her.

But as I heard from a member of the Republican National Committee, Diana Orrock in Nevada, maybe it was the only way.

She, a Trump supporter from the start, says that in the event of his defeat, the party as we know it should die.

Image caption Diana Orrock, Republican National Committee member says if Trump loses, she predicts a severing of ties from the old party mainstream

She predicts, of course, a Trump landslide (citing the Brexit vote, like so many Trump supporters, as evidence of tidal wave politics) but all the evidence is against her. She is well aware that the party professionals who live by opinion polls believe his chances of success are now very slim.

Therefore, she's happy to talk about the aftermath of defeat and contemplate a severing of the "Trump movement" from the old party mainstream, whom she dismisses as "globalisers" who might as well be Democrats.

Spiral of insults

It is very unlikely to happen like that, because the American parties have always been sprawling coalitions who've survived by holding enemies together. But the forces unleashed by this campaign - across the country - aren't going to subside.

"Corruption" is one of Mr Trump's favourite words. He is aware that Clinton's misjudgements and mangled explanations over her private email server trouble many Americans who'd usually support her without question, and the result is a debate that has plumbed the depths of insult.

Image copyright Getty Images Image caption Donald Trump continues to say the establishment is out to get him

In the debate last week, Mr Trump accused Bill Clinton of rape, no less, and to his face. And he's engaged himself in a running argument with a group of women (nine at the last count) who've accused him of improprieties, all emphatically denied. So the spiral takes everyone down.

Distrust, even hatred, is embedded in this campaign in a way that none of us has seen in recent times.

Many voters are bewildered and dismayed by it, but others - on both sides - are enthusiastically adopting the tone, and the consequence is that the very thing both candidates say they aspire to bring to an end - mistrust and gridlock on Capitol Hill - is likely to intensify, however the votes fall on 8 November.

No compromise

For Latinos I met in Las Vegas, organising through the Culinary Workers Union against Trump (who has a hotel here, and refuses to recognise the union), or for conservatives who are fearful of Supreme Court appointments under a Clinton presidency, the result is the same: Stand-off.

Neither side can trust the other. Trump's campaign has been based on the notion that compromise is always a dirty word, and never will be anything else. Do the deal, and give no quarter. That's the way.

Image caption The Culinary Workers Union is not allowed to operate in the Trump Hotel in Vegas

And the frustration on Mrs Clinton's side is that the dragon that she claims is Mr Trump - certainly the most divisive candidate the Republicans have nominated since Goldwater in '64, and without his beguiling straightforwardness - is not slain.

That's what gives some Republicans hope, though they are certainly not now a majority in the party.

With Democrats making a big push, for example, to win in Arizona - unthinkable a few months ago - and a steady drift in the polls against him, Mr Trump's options are now narrowing painfully.

What is his hope? More trouble for Mrs Clinton from Wikileaks, is certainly his best bet.

He needs an event from outside, because inside his campaign it looks as if the wagons are being pulled into a circle for the last stand.

The consequence is a debate that may be as dramatic as any of the big fights for which Las Vegas is famous.