Labour Party leadership candidate Jeremy Corbyn gestures with supporters during a rally in London on Sept. 10. (Peter Nicholls/Reuters)

A white-haired socialist comes out of nowhere to electrify the grass roots and upend the political establishment, winning the leadership of his center-left party by defeating better-known rivals, including a woman who would have made history.

For the legions of avid fans of Vermont Sen. Bernie Sanders, this is the dream scenario in his uphill contest for the Democratic Party nomination against Hillary Rodham Clinton.

But for the diehard backers of Britain’s Jeremy Corbyn, this is likely to be the joyful reality come Saturday morning. And for the many critics within his own party, including former prime minister Tony Blair, it is a nightmare come to life.

The Labour Party — which has spent a century trading power with the Conservatives and governed this country as recently as five years ago — appears set to select Corbyn as its new leader on Saturday as it continues to reckon with its disastrous loss in May elections.

The pick would have been unimaginable even several months ago but now appears a foregone conclusion judging by polls showing him running away with victory in a contest against three more centrist challengers.

Labour Party leadership candidate Jeremy Corbyn, center, applauds the audience and supporters during a rally in London Friday. (Peter Nicholls/Reuters)

It is not difficult to be more centrist than Corbyn: His unapologetically leftist views — he favors a British exit from NATO, renationalization of the railway and energy industries, and a possible war-crimes trial for Blair — have long placed him outside Labour’s mainstream establishment.

Yet a victory on Saturday would be just the latest marker of an extraordinary transformation of the political left, one that is fueled by disenchantment with the traditional parties and their leaders following the failures of the Iraq War and the Great Recession. It is on display this year not only in Britain but in countries across the Western world.

In Greece, the Syriza party became the first radical leftist party to govern in the European Union by sweeping to victory in January. In Spain and Ireland, left-wing parties are defying history by vying for a kingmaker role in elections later this year and early next. In Scotland, nationalists dethroned the Labour Party, which had been dominant for decades, by casting Labour as too timid to take on the ideology of austerity.

Riling the left

But it is in the United States where Corbyn’s rise may have the most resonance, coming as Sanders tops Clinton in New Hampshire polls and pulls even in Iowa.

Like Sanders, Corbyn is trying to foment revolution from within by seeking to tear down an existing party establishment that both men see as too cozy with big business and too prone to military adventurism overseas.

Although Sanders remains a long-shot in the eyes of most political commentators, Corbyn was seen in exactly the same light until a barnstorming tour this summer in which he energized crowds across Britain and went from quixotic voice in the wilderness to prohibitive favorite.

“It’s totally astonishing,” said Alex Callinicos, a European studies professor at King’s College London.

Callinicos said he lives in the bearded 66-year-old’s parliamentary district and knows him to be “a fine individual, modest, says what he means.”

But a leader of one of the country’s two main parties?

It never would have crossed Callinicos’s mind were it not for the broader forces now roiling the left, just as they have on the right for several years.

“What we’re seeing is the emergence of new movements on the left that reject austerity and want to renew what are seen as corrupt and unresponsive political systems,” Callinicos said. “Corbyn has benefited from that.”

A win would put Corbyn in line to become Labour’s candidate for prime minister in the next election, in 2020. But more immediately it would give him a weekly chance to joust from a distance of two sword-lengths with the incumbent, David Cameron, at the unparalleled political carnival known as Prime Minister’s Questions.

Corbyn’s backers relish that opportunity, believing it will draw the sharpest possible contrast between the traditional party of the working man — Labour — and a Conservative-run government that they see as favoring the wealthy.

Corbyn, who represents a posh area of north London and who has been in parliament since 1983, favors ditching austerity policies that have reduced the size of government and advocates tax hikes for the rich, as well as an end to loopholes for corporations.

“We change politics in Britain, we challenge the narrative that only the individual matters,” Corbyn, dressed with typical informality in a yellow, open-collar shirt, told his supporters in the campaign’s final rally on Thursday evening. “And instead we say the common good is the aspiration of all of us."

But as he does face-to-face battle with Cameron, Corbyn will have to watch his back, given the hostility that some in the party feel toward his prospective leadership.

Blair said in July that anyone whose heart is with Corbyn should “get a transplant.”

The former prime minister has only toughened his stance since then, writing in the Guardian that a Corbyn victory would mean “annihilation” for the party that Blair led for 13 years, including for a decade at 10 Downing Street.

“Please understand the danger we are in. The party is walking eyes shut, arms outstretched over the cliff’s edge to the jagged rocks below,” he wrote. “This is not a moment to refrain from disturbing the serenity of the walk on the basis it causes ‘disunity’. It is a moment for a rugby tackle, if that were possible.”

But Blair’s blasts only seem to have strengthened the resolve of Corbyn, and his backers, to shake up a party that had lurched toward the center under Blair’s New Labour vision.

In many ways the union-backed Corbyn appears to be a throwback to a pre-Blair, 1980s version of the Labour Party, one that held firm to its left-wing beliefs but consistently lost to Margaret Thatcher.

Key Corbyn positions include the renationalization of vast sectors of the economy and unilateral nuclear disarmament. Those stances help to distinguish him from his more mainstream challengers, none of whom have captured much public excitement despite the fact that two, Yvette Cooper and Liz Kendall, are vying to become Labour’s first-ever female leader.

Tony Travers, a political scientist at the London School of Economics, said Corbyn represents something that voters on both the left and right increasingly seem to crave as the problems facing the world’s leaders only multiply.

“It’s a cry against the complexity and difficulty of the modern world, and a desire to have simpler answers,” Travers said. “What people are looking for is the nonestablishment offer.”

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