In many ways, the United States Constitution and the entire American experiment can be argued to be the supreme products of the Age of Reason.

From its birth, America has been a society predicated on enlightened principles, one that has continuously evolved as it has strived to realise the “more perfect union” envisaged by its founders.

This evolution hasn’t, of course, been seamless or without great human cost. It’s occurred in a sometimes halting, fits-and-starts manner over the course of 240 years.

But throughout that time, America has managed to maintain a forward and progressive momentum, always inching ever closer to fulfilling its original promise to all of its people.

So why, the rest of the world is asking, are so many Americans now seeming to embrace unreason as personified by the deeply troubling Donald Trump in the run-up to this November’s elections?

The 2016 primary election season came to an end last night in California, formalising the businessman and professional self-promoter’s once unimaginable lock on the Republican presidential nomination.

It was the undramatic and long-anticipated epilogue to an unprecedented insurgency campaign, one that resulted in the mainstreaming and political legitimisation of a denizen of the outermost fringes of American crackpottery.

Trump’s serial recklessness and blasé contempt for convention, political propriety and even objective facts, which have the temerity to run counter to his blustering pronouncements, have gone from provoking mirth to prompting increasingly deep concerns on both political and substantive grounds. Any laughter you hear about the man now is likely to be of the decidedly nervous variety.

Any one of numerous inflammatory outbursts caused by his rampant political form of Tourettes, for instance, would have been sufficient to disqualify any other putative candidate months ago. Where Trump is concerned, though, whatever did not kill his candidacy simply seemed to make him stronger.

Given he will be facing the competent but uninspiring and supremely unlovable Hillary Clinton — also confirmed as the Democratic Party’s nominee last night — in November, many are now pondering what once seemed unthinkable: the prospect of a Trump administration being sworn into office next January.

History would seem to preclude such an eventuality. But then history also appeared to preclude the possibility of Trump emerging from the primaries as the Republican standard-bearer. Even now an embarrassed but shameless party establishment is closing ranks behind the man they were deriding only weeks ago as, among other things, “an embarrassment to the Republican Party”, “a madman who must be stopped”, “a delusional narcissist and an orange-faced windbag”, “a cancer on conservatism” and even “our Mussolini”, despite his proclivity for making questionable public statements and employing repellent racial and religious stereotypes remaining entirely undiminished.

To some, he is the bad-haired, big-mouthed monster from the id of the Republican Party’s extreme wing, giving strident voice to long-suppressed cultural resentments and animus, and myriad post-recessionary economic and social frustrations.

For them, Trump is the inevitable reductio ad absurdum of the Republican establishment’s politically expedient but always dangerous flirtation with social and cultural zealots in recent decades. They view him as the embodiment of a particularly ugly form of political brutalism or what could be termed “strongmanism”, common enough in many other countries that have gone through prolonged periods of economic and social upheaval, but entirely new to the American experience, at least at such an elevated level.

To others, he’s simply an unscrupulous showman, a man bereft of all guiding principles and instead driven by an insatiable need for self-aggrandisement. Whether he himself is a bigot, a racist or a misogynist is ultimately immaterial, these commentators contend.

What’s important is that, like all true opportunists, he has no qualms about making use of others’ intolerance to serve his own political ends. And Trump has routinely and brazenly exploited racial, religious and cultural tensions in the US from the very day he announced his presidential bid, a candidacy seemingly so far-fetched and so very foredoomed that few took it seriously until he began racking up primary and caucus victories this year.

Of course, Trump benefited immeasurably by running against so large and lacklustre a field in the Republican primaries.

Then his manufactured celebrity, his ability to make himself stand out from the pack, even if only in terms of his deliberately cultivated outrageousness and his undeniable expertise at dividing opponents to conquer — often only by hair’s-breadth pluralities — proved to be of considerable value when he was facing up to 16 other contenders.

In the one-on-one contest he faces now, however, he will be scrutinised, analysed and criticised as never before.

And he will have to demonstrate a mastery of more than just crude generalisations and snide insults if he is to have any possible chance of prevailing in the general election.

He is now the presumptive Republican presidential candidate, after all, not a seat-of-your-pants outsider running a vanity campaign as outsized as his ego.

As an insurgent on his party’s primary campaign trail, he had the luxury of being able to be openly contemptuous of the complexities of political and economic processes while running against establishment names closely identified with Washington gridlock, stagnant wages, declining social mobility and a dwindling US manufacturing base.

He won applause and votes by playing to the more marginalised elements of the Republican base, those who felt most dissatisfied and neglected, by repeatedly expressing fire-and-brimstone impatience with the finer details and nuance of statecraft.

But socioeconomic and political realities cannot be ignored or simply insulted out of existence, particularly by the occupant of the Oval Office. Reality, after all, is that which does not go away just because you stage a tantrum and refuse to believe in it.

It’s been said of Trump that this “Master Persuader was able to continuously warp reality until he got what he wanted” in the primary elections.

He will find this a much harder feat to pull off in the general election campaign when he needs to put together a demographically, culturally and geographically disparate nationwide coalition to prevail at the polls. He will also, of course, require an outright majority of the votes cast to be elected in a one-on-one matchup, not the simple plurality of party members sufficient to secure him the GOP nomination in a very heavily contested field.

Given his demonstrated ability to insult and to alienate some of the very constituencies he will require to put together such a grand coalition — women, Hispanics and even many other Republicans — the odds of Trump being able to seal this particular deal with the American people are probably on the same order as those of Bermuda playing in the next World Cup final. And winning.

And that is why those in Bermuda concerned about the prospect of a Trump presidency probably needn’t lose too much sleep, at least not just yet, and conclude the unique and always improbable American experiment is about to end in failure.