The worst mistake the centre left across the world could make now is to confuse what happened on Tuesday with the inevitable. 

Instinctively, in the aftermath of a huge political event, we retroactively impose the coherent narrative structure that frames it in a grand historical context. 

In doing so, we always overlook the part played by accident.  So if you are tempted to see Donald Trump as a gigantic wave in a tide of reactionary horror that will never ebb, please don’t.  His victory was not inevitable.  It should not be read as proof that America is terminally racist, or that the future belongs to the populist right, or that Martin Luther King was wrong about the long arc of moral history bending towards justice. 

Trump won for a complex range of reasons: some profound, but more arbitrary. 

Michael Moore: Trump will 'break laws'

In the US, as here, the political class has failed to gauge the strength of working class white resentment towards a smug elite and its apparent indifference to the wage stagnation created by outsourced jobs, cheap migrant labour, and the snaffling of almost all growth in GDP by the wealthy.  This was profound. 

Also profound was racism’s part in turbo-charging Trump’s insurgency, though one shouldn’t exaggerate its hold on the US electorate when Obama, whose approval ratings are in the mid-fifties, would have been re-elected but for the 25th Amendment’s pesky two term limit. 

With this result, the accidentals far outweighed the fundamentals.  But for the random tragedy of losing a son to cancer, Joe Biden’s authentic voice as the patron saint of hardscrabble America would have made him the President-Elect.  Had James Comey, the FBI director, not gone rogue with the 11th hour reopening of Hillary’s deplorable basket of emails, she would have won. 

That she’s on course to win the popular vote by an eerily similar margin to Al Gore’s in 2000, is not proof of a dramatic lurch to the right.  It is evidence that the United States remains as evenly split as it has been since the turn of the millennium. 

The fact that Trump’s victory is more an aberration than confirmation of the Marxist view of history as the unstoppable sweep of economic forces, hardly makes its potential for damage any less alarming. 

But it does make it less sinister in the sense that it can quickly be reversed.  If Trump fails to recreate America as an earthly paradise within four years, as he might, a fresher Democrat with a more resonant message than Hillary’s “Hey, guys, I’ve hung around for like a million years, so come on, gimme a break” will probably reclaim the White House in 2020. 

By the crudest statistic, Britain is precisely as evenly split as the US.  At the last election, the combined Tory and Ukip vote was almost identical to the aggregate for Labour, the Lib Dems, the SNP, Plaid Cumru and the Greens. 

If we live in an effective one-party state, that’s due in large part to the vagaries of a crazy electoral system.  Should the Tories win the anticipated landslide in 2020 (assuming Theresa May doesn’t go to the country early for a Brexit mandate), a realignment of the opposition - whether as an electoral pact between the centrist party created from the ashes of Labour and other centre left parties, or as a formal confederation - would be inevitable. 

Led by a politician with empathy with disaffected traditional Labour voters and the language to communicate it, such an alliance would reinvigorate progressive politics. 

Of course, 2020 is an aeon away in domestic and geopolitical terms.  What now looks like a finely balanced see-saw between the forces of reaction and progress might be tilted decisively next year by the election of Marie Le Pen in France and an anti-immigrant German Chancellor. 

But narrow electoral wins for Brexit and Trump are not reason to reimagine the democratic west as sliding irreversibly towards neo-fascism.  They are twin sirens warning against the folly of smugly assuming that history will continue on the same trajectory without careful steering. 

“The path this country has taken has never been a straight line,” said Obama last week after meeting his successor in the Oval Office. “ We zig and zag and sometimes we move in ways that some people think is forward and others think is moving back.  And that's OK.” 

Well, this is one helluva zig, and it’s not remotely OK.  But nor is it over until the tangerine fat man punches in those codes.  The American centre left has no more time to waste on infantile “Not My President” self-indulgence than its British equivalent has in whining about Jeremy Corbyn’s legitimate mandate. 

What Boris Johnson, in a diplomatic term presumably borrowed from Lord Carrington, calls the “whinge-o-rama” needs to end without delay on both sides of the ocean.  The progressive future we risked by complacently thinking it was guaranteed won’t be rescued by cry-babies.  It will take grownups that understand and speak to the alienation that drives swathes of the electorate to succumb to the worse angels of their nature.