I laughed last June, when that orange ignoramus, with his ridiculous hair and impossible pomposity, descended the escalator into the lobby of Trump Tower in New York to the tune of Neil Young’s “Keep On Rockin’ In The Free World”.

We all did, didn't we? It was impossible not to. He radiated smugness and pomposity with an intensity that would break a Geiger counter. He was preposterous. But there he stood, announcing his candidacy for president and then immediately turning to call all Mexican immigrants “rapists”.

Time and again, journalists and analysts expressed with great certainty that one cretinous gaffe or another would finally put Donald Trump’s rickety, ridiculous, idiosyncratic campaign into a tailspin. He lied, and lied, and lied. His contempt for the truth, and for the constitution of the United States, was breathtaking – and matched only by his wilful ignorance of both.

This was a bubble and, received wisdom held in the summer of 2015, it would burst soon enough.

But our laughter was premature. For more than a year, to the disbelief, especially, of America’s media and political elites, Trump defied all the laws of political gravity. Every insane utterance seemed to boost, rather than hinder him. Written off by everyone as a joke, the orange juggernaut blundered on to win handily in the primaries.

This week, that longed-for tailspin seems to have finally arrived. Having goaded the news cycle, bare-facedly telling lie after madcap lie, Trump’s quittance is, maybe, finally here.

His behaviour recently fits the theory that Trump himself is engaging in self-sabotage, terrified by the prospect that his Quixotic tilt at the presidential windmill might end up, against all reason, succeeding. If this is the case, he's doing a bang-up job.

The beginning of the Democratic National Convention in Cleveland saw Trump and Clinton almost neck-and-neck in the polling, according to FiveThirtyEight’s aggregate. Now, just two weeks later, Trump’s chance of victory has plummeted to just 11 per cent . He is imploding; behind in every poll in every single key swing state, often by double-digits.

Trump’s nemesis appeared in the form of the parents of Captain Humayan Khan, a Muslim-American US marine who had been killed in combat in Iraq, who addressed the DNC. “Have you even read the US constitution,” Khan’s father Khizr demanded to know, brandishing his copy of the document as he addressed the Republican nominee directly.

The moment was exquisitely choreographed to inflame the thin-skinned Trump, and it worked a treat. “What right does he have to stand there in front of millions of people and say I haven’t read the constitution,” Trump said, in perhaps the finest unintended First Amendment joke in history.

It was the starting-gun for a fortnight of farcical self-immolation.

The following day, Trump fluffed an interview with ABC, saying that Putin was “not going to go in” to Ukraine, seemingly unaware that Russia had already annexed a large part of it in the Crimea. He hit out at – of all people – fire safety marshals, hinting that they were part of a conspiracy to deny people access to his rallies. Then, he had to be rescued by the same fire marshals when he got stuck in a lift at a rally in Colorado Springs.

In an act of breathtaking political cattiness, he undermined two party grandees – speaker Paul Ryan and former presidential candidate John McCain hinting that he was “just not there yet” to support the former, purposely echoing Ryan’s own havering on whether to support him earlier in the election cycle.

On Tuesday, in a press conference, the property developer set off another furore when he appeared to hint that “second amendment people” should attempt to assassinate Hillary Clinton. On Thursday, he got the day wrong - twice saying that it was Friday. And throughout it all, he continued his ill-fated attacks on the Khan family.

Meanwhile, as Trump went to bits in the national spotlight like damp tissue paper in a force 9 gale, his campaign was also floundering, failing to even attempt the basic infrastructure needed to turn Trump's activist base of support into anything like the kind of coalition necessary to win key swing states like Pennsylvania, Ohio or Florida.

He is being outspent not just by the Clinton campaign, but also by the third-party bids of Libertarian Gary Johnson and Green Party nominee Jill Stein. Field offices are vacant. Campaign positions remain unfilled. The campaign lacks even the bare bones of infrastructure in any key swing state, and confusion reigns as to who's in charge of what.

Trump may have hoped that the Republican National Committee would pick up the slack in the ground-game that he himself clearly can’t be bothered to run, but RNC officials are beginning to hint that the party might cut off its errant nominee completely, focusing on down-ballot races instead.

This week it has become starkly clear that Trump’s personal delusions are metastasizing. All hope for a “pivot” towards presidential behaviour by the brash property developer – hope that was, in all honesty, pretty dim to start with – is now gone, drowned in the flood of loosely-contained stream-of-consciousness bigotry and random petty recrimination.

The most auspicious sign of things to come is in the reaction of Trump to his own implosion. Predictably, it has not been one of self-examination; of course, Trump could never be at fault. It’s the media’s fault. “If the disgusting and corrupt media covered me honestly and didn't put false meaning into the words I say,” he tweeted churlishly on Sunday, “I would be beating Hillary by 20 per cent”.

The article that drew his particular ire was a New York Times piece from Saturday that took a close look at the Trump campaign and found it cracking under the pressure. “The effort to save Mr. Trump from himself,” the authors wrote, “has plainly failed.”

The candidate’s long-standing contempt for media coverage rose to fill the gap; Trump flirted publicly this week with the idea of adding the New York Times to the list of publications, like the Washington Post, which have been barred from his rallies. On top of that, he added a troubling new trope: that, if he were to lose, then a rigged system would be at fault.

The idea that the political system in the US is rigged has been a constant in the 2016 election cycle; Bernie Sanders made as much hay from it as Trump has. But if Trump’s disaffected core support are told, over and over again, that the election is going to be stolen from them, then this nightmare fever-dream of an election may yet have more horrors in store for us.

In the meantime, it is looking like this might finally be the end for the Republican party’s ill-fated Trump experiment.

But then, we’ve all been wrong about that plenty of times before.