If Trump were a film character – and certainly not any played by Robert De Niro – it would be the Terminator: Republican, sort of, and impervious to the blows that would fell an ordinary human being.

St Louis should have seen the beginning of his political demise. He ascended the stage for the second debate in one of the weakest positions ever faced by a presidential candidate. Just days after revealing a breathtaking misogyny, he should have been easily dispatched by a formidable female candidate. But Hillary Clinton could not land the killer punch.

She plugged away, sometimes diligently sometimes dully, but never decisively. Trump simply refused to lose.

Amazingly, The Apprentice video tape from 2005 was not the kiss of death. Instead, after an apology of sorts, it became clear how he would exploit it. The 'locker room' banter (his description) was yet more evidence of Trump's political incorrectness. The fact the tape exists is evidence not of his hatred of women, but of his authenticity.

It is this quality – whether or not you believe he is faking it – that so appeals to the disaffected, predominantly white, non-college educated men that drive his campaign – his 'movement' – forward. We have reached a moment in American politics where there is nothing he could say or do – perhaps (in the words of former Louisiana governor Edwin Edwards) not even being 'caught in bed with either a dead girl or a live boy' – that would force him from the race or him from the affection of his supporters.

This has been called 'immunity by profusion'. Trump talks such recurrent nonsense that he is never held to account for any one single piece. This strategy should have come unstuck with the release of the 2005 tape – but hasn't. It contains nothing that his supporters won't readily forgive or some actively admire.

His entire campaign has been built on repudiating the phoney morality, double standards and foreign and economic policy mismanagement of the political elite of which Clinton is the embodiment. Trump's own immorality pales against the disastrous wars and a ruined manufacturing base that the elite has delivered up.

He does not have to be right in this analysis to be effective in propagating it. His campaign is not about to become an apology tour. He says sorry minimally, as he did in St Louis, before returning to a crude but effective offense that no amount of debate rehearsal by Hillary Clinton has been able to effectively check.

He strode onto stage and refused to shake his opponent's hand. There is a rule in presidential politics that when you are coming to make peace you wear red. This aggressive colour balances against the passive message. When you come to make war, however, you wear blue. This makes your belligerence seem tempered and rational.

Trump deliberately broke this rule. He came out swinging in a blood red tie. Hillary wore blue and couldn't land the punch she needed to. Trump, we all expected, would be chastened by the video revelations. What we learned is that Trump does not do chastened. Within minutes, he was telling her that 'you ought to be ashamed of yourself,' for 'acid washing' 33,000 emails.

He stuck to his mantra: politicians like Hillary were 'stupid' for getting into Iraq and 'stupid' for leaving it too quickly. They created ISIS. They cut trade deals that reward Mexicans and Chinese. He told her she 'should be in jail' and that as President he would try to put her there. All this before he then claimed he was 'a gentleman' for letting her answer a question first.

Trump's was an extraordinary performance, impervious to facts and political realities. He even managed to appropriate 'honest' Abraham Lincoln in an attempt to paint her as a serial liar, "with tremendous hate in her heart".

Hillary did as well in the face of all this as we expected her to – but no better. She was well-rehearsed. She did not lecture or hector. She displayed an impressive grasp of technical details, especially on healthcare and foreign policy. Her resume was invoked to expose the paucity of his. She flattered Trump's children to demonstrate her warmth.

And yet none of this could dent Trump's bravado unchained. He simply refuses to become a conventional candidate. He must surely lose in November but he will not lose by diluting his brand. He understands that the appeal of the Terminator character is its relentless perseverance. That is what accounts for its and Trump's unsettling box office appeal.

Timothy J. Lynch is Associate Professor in American Politics, School of Social and Political Sciences, University of Melbourne. He is part of a four-part masterclass series in the Faculty of Arts assessing pivotal elections in US history.

This article was co-published with the University of Melbourne's Election Watch and the Herald Sun.

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