Jeremy Corbyn and Donald Trump are cut from the same cloth, as we’ll see in this week’s by-elections

The plastic surgeon hasn’t been born, nor the fairground mirror built, that could make them ringers. Yet the more you are exposed to the transatlantic double act of Donald Trump and Jeremy Corbyn, the more they begin to resemble Bizarro World reflections of each other.

Some of the more familiar similarities include the skilful harnessing of their bases’ rage against the status quo to power them to insurgent victories. In geopolitical terms, each is pro-Russia and anti-Nato, anti-globalisation and protectionist. Personally, meanwhile, they are a touch brittle when challenged by the media they innately distrust.

There are also distinctions, of course. The Washington carnivore in the White House is itching to fire a nuclear warhead, while the Islington herbivore never would. So far as decency, honesty, skin tone, hand size and anything else of a vaguely non-political nature goes, they could hardly be more different. You can no more easily picture Corbyn grabbing a woman down there, than Trump boiling up a vat of damson jam. Beyond being thrice married, currently to a foreigner, they may have literally nothing in common.

But diametrically opposite characters can be flip sides of the same political coin, and recent events crystallise the similarity which may explain why each was always doomed to fail.

It is not the shared accusation about tolerating anti-Semitism, or being leadership amateurs who stagger about in a fog of chaos. Nor is it that Trump’s inability to hire or retain key staff echoes the zany game of shadow Cabinet musical chairs over which Corbyn has expertly presided.

It isn’t that each is extraordinarily isolated. With almost no genuine support from his party’s elected representatives, each is sustained by a tiny coterie of apparatchiks – and defended by an angry base with no tolerance for dissent that threatens de-selection or a primary challenge against any Labour or congressional Republican who refuses to kiss the ring.

The most significant bond between Corbyn and Trump is that they, more than any Western leaders in memory, are Greatest Hits politicians. Lacking the will, imagination and energy to produce new material, all they do is belt out the tunes that won the fans over in their first place.

We saw it last summer when Jeremy Corbyn was challenged by Owen Smith, and seemed happy for the first time since being elected when he pleasured the faithful with the hits that won him the job first time around.

And we saw it last weekend when Trump held that “campaign rally” in Florida. After the turmoil of losing Mike Flynnski to The Washington Post and having his Moos-lim ban stayed by appeal court judges, he also seemed happy for the first time since being inaugurated as he rattled out his stump speech riffs about media deceit, the Mexican wall, and so on. He even threw in a whopper to keep the kids happy, though the source of that Swedish terrorism claim remains a mystery.

And this is what weak people always do when they are flailing about, way out of their depth. They scurry back to the comfort zone and turn to their most slavish admirers for reaffirmation.

It’s what Ricky Gervais’s character did in Extras when depressed by hideous reviews for his imbecilic, racist, catchphrase-laden sitcom. Humiliated when forced to parrot “Are you ’aving a laff” for a fan down the pub, he flees to a nightclub and moans about his unfair press to David Bowie. Bowie replies by ridiculing him in song (“He sold his soul for a shot at fame …See his pug-nosed face”). Stratospherically out of his celebrity league, Millman goes back to the pub to bathe in the love of the idiot fans he despises.

This is exactly why Trump held his rally. Smart arse liberals who watch CNN and read the New York Times might hate his act, like broadsheet reviewers hated Millman’s When The Whistle Blows. But the rubes down in Florida, like the oaf in Millman’s boozer, still love him, his racist gags and mind-numbing catchphrases.

Yet a political fan base is as fickle as any other. As Bowie understood better than most, you cannot play nothing but the old hits and stay relevant or in vogue. If you don’t widen the base with fresh material, it will contract as some of the existing fans get bored and drift away.

Already, Trump’s historically dismal approval ratings (38 per cent in one poll) suggest he is losing some of his. Corbyn’s reportedly weakening hold on his could be tested again if a Labour loss in either of Thursday’s by-elections (let alone both) sparks the annual leadership challenge.

More gifted politicians would read the runes and adapt. These two cannot. Driven by their absolute certainties to mistake adaptability for weakness, forced by insecurity to confuse unpopularity with martyrdom, they have no capacity for reinvention.

Corbyn always sounded more like one of those old chart acts that play nostalgia weekends at Butlins than a contemporary artist. After less than a month, Trump’s rally hinted at the same.

He and the fan club have taken the Republican Party hostage, but if his base dwindles dramatically it will no longer be able to terrorise Senators and Representatives into doing his will. Perhaps it was his fear of the Stockholm Syndrome losing its grip that drew Trump’s addled mind to Swedish terrorism?