Jeremy Corbyn has the professional politicians, journalists, and think-tankers who dominate conventional British politics bewildered. Ever since his stratospheric ascent during the Labour Party leadership campaign and subsequent triumph, he has upended all the rules of the twenty-first century neoliberal settlement in one of its heartlands — the Britain that gave the world Thatcherism, and later the template for Thatcherite governance by a social-democratic party, Tony Blair’s New Labour.

And it’s not just those within the Westminster bubble who have had their assumptions confounded by this development — the British left has as well. In recent years, the only parties of the European left showing any signs of life have been those outside, and to the left, of the classical labor movement, particularly Greece’s Syriza and Spain’s Podemos.

Doomed by their acceptance of austerity and struggling to reconcile their enduring attachment to the capitalist state with its diminishing ability to deliver meaningful social reform, the old parties offered studies in collapse (Greece’s Pasok), coalition with the Right (Germany’s Social Democratic Party), or futility (France’s Socialist Party).

Britain remained more or less immune to the charms of further-left politics. The main left alternatives in the 2015 election, Left Unity and the Trade Unionist and Socialist Coalition (TUSC), secured votes that varied from the negligible to the invisible. Neither of the arguments that underpinned these ventures — that the Labour Party was a lost cause and that Britain needed its own version of Syriza — look any more robust now, to put it mildly, than they did when voters spurned them in May.

A socialist takeover of Labour was a script from which no one was working. Even Ed Miliband’s timid efforts to move the party beyond full-blown Blairism seemed more than the electorate could bear. And while Labour secured modest gains in England in the 2015 general election (at the expense of the Conservatives’ erstwhile coalition partners, the Liberal Democrats), this was easily wiped out by a trouncing in Scotland courtesy of a Scottish National Party that had positioned itself to Labour’s left.

But rather than heralding the Blair faction’s return to the leadership — from which it had been no more than partially displaced by Miliband in 2010 — Labour’s general election defeat led instead to an unexpected left-wing insurgency that was, astonishingly, victorious.

Corbyn, a backbench Labour member of parliament (MP) since 1983 who had never sought senior office in his party and who was best known as a roving tribune for the Left and its causes, won by a landslide, and in all categories of the leadership electorate — individual party members, affiliated trade union members, and registered supporters.

Originally, the unabashed socialist had run simply to broaden the debate within the party. Indeed, he only secured a place on the ballot paper because a number of MPs who did not support him lent him their nominations out of sympathy or calculations of expediency.

The governing paradox of this episode — and what makes Corbyn’s victory so fragile, his historic mandate notwithstanding — is that it comes at a time of great weakness for the British left. The last time the Left surged to within sight of the Labour leadership was in the 1979–1983 period, when Tony Benn headed the movement for change. The differences between then and now are instructive.

In the earlier period, the labor movement was a deeply entrenched force in British life. Trade union membership was twice as high as it is today. The connections between work, community, and worker organization, though already attenuating, remained powerful.

The unions themselves operated under the leadership of a left strongly influenced by a thirty-thousand-strong Communist Party that, although small compared to its fraternal parties on the continent, was huge compared to today’s far-left groups.

And within Labour, there was a strong cadre of genuine socialist MPs, an important asset in a party marinated in parliamentarism. Corbyn, today an almost lone survivor of the Blair assault on the Left, hardly stood out in 1983.

The movement of the early 1980s ran through the established grooves of the labor movement, shaped by a century of struggle. It drew plenty of new people into politics, but it was the politics of the branch meeting and union elections, of Labour Weekly and Tribune, of rule book changes and parliamentary caucuses.

To be sure, there was pressure from progressive groups outside the traditional movement. But for the most part, the Left sought to advance their agenda by relying on organized labor’s strength and mobilizing capacity.

The intervening thirty years have seen the destruction of that world along every axis. And yet, this summer, the Left won — securing for Labour the most left-wing leader in party history not through arcane maneuvers but the votes of 250,000 citizens.

While the Corbyn movement has come from a somewhat different place, it has advanced beyond the Left of Benn. It has done so by synthesizing what remains of the traditional labor movement with the new movements of the last twenty years, channelling the mobilizing strengths, and many of the people, associated with twenty-first century “movement” politics through the embedded structures of the country’s traditional left.

In Britain, the classic example of movement politics is the antiwar movement, which at its peak reached dimensions that are hard to credit today. Sustained mobilization on the streets and in communities resulted in Britain’s largest-ever demonstrations (by several orders of magnitude) and the largest-ever revolt against a government by its own MPs. But it failed to stop the attack on Iraq.

From my view — as chair of the Stop the War Coalition from 2001–2011 and again today, with Corbyn having served in between — there is one principal reason for this failure: the lack of a powerful labor movement capable of giving the antiwar sentiment expression in workplaces and elsewhere the antiwar movement could not reach.

That Tony Blair was a Labour prime minister made it difficult to energize the top ranks of the trade unions. But the problem went deeper than that. The strength of trade union political activism (outside routine electoral duties) was atrophying, and without it, the antiwar movement lacked the means to break the front-bench parliamentary consensus for war.

Corbyn has embodied the push to overcome that disjuncture ever since. A Labour MP who engaged in Stop the War from the start, his road to victory this summer began on February 15, 2003 when he addressed the two million people who marched in London against the Iraq War.

There are, of course, differences between Stop the War 2003 and Corbyn 2015. But both tapped into a huge constituency of people not engaged in regular politics, who hold broadly progressive views, and who can leap into action if it seems productive to do so. Elite politics today has mostly passed them by, and they have generally returned the favor. Yet when they perceive a crack in the edifice of day-to-day politics — when political activity offers plausible hope of making an immediate difference — they can rush in, to profound effect.

The Labour Party’s leadership elections produced such a crack. The question of who leads one of the country’s two traditional parties of government is a consequential one, affecting people’s lives in a way that, say, a plan to unite various far-left factions in an electoral front typically does not. And Labour made it relatively easy to get involved, while offering a range of allies.

This activated base of support hasn’t obviated labor’s importance, however. Trade union funding and logistical support propelled Corbyn during the campaign, and the labor movement continues to be an orienting force in post-election efforts. The first two major initiatives carried out by Momentum, the official successor body of the Corbyn campaign, were to take to the streets to register people to vote and to take to social media to lobby against British bombing of Syria, both also union concerns.

While none of this solves all the problems of socialist political advance, it does offer a more fruitful model for taking movement politics into the mainstream than any of the others on offer.

Looking across the advanced capitalist world, the Corbyn movement, the new left initiatives across Europe, and the Bernie Sanders campaign in the US share some common objectives. These include opposition to austerity policies that place the burden of the economic crisis on the backs of the poorest and weakest; revulsion at imperialist war; and a desire for a “different kind of politics,” as opposed to the antiseptic rituals of the elected political elite.

This new politics is generally more class-focused than class-rooted. While it places issues of social inequality and global economic power front and center, it neither emerges from the organic institutions of the class-in-itself nor advances the socialist perspective of the class-for-itself.

Nevertheless, in Britain this movement has doubled the Labour Party’s membership, such that it’s now larger than every other party in the country combined, and something like sixty or seventy times the aggregated strength of all further-left groupings. This is a real step towards reengaging masses of people in the struggle for socialism in the contemporary world.

Still, questions both profound and longstanding remain for the British left. Can the Labour Party be a vehicle for establishing a socialist society? Can socialism be won through the winning of a parliamentary majority? And what would this socialism look like?

Corbyn’s victory is a clear indication that the terrain of battle still includes the Labour Party. Despite the flood of new members, his position as party leader is quite precarious, with the threat of a coup against his leadership ever-present and perpetually stoked by residents of the “Westminster bubble.” Every other day, it seems a new plot is hatched, with different putative procedures and standard-bearers.

The base for this frenzy is the Parliamentary Labour Party, where committed Corbyn supporters number no more than 10 percent of the membership. Such dissension is inevitably reflected in the shadow cabinet, the couple dozen parliamentarians who constitute the party’s effective daily political leadership.

The majority ache for a return to politics as usual. Some may remain loyal despite misgivings, but many will not. They are strong not because of any great desire for a second dose of New Labour government, but because they have the backing of the ruling elite, the state, and its organs of power — including a mass media that was intensely hostile to Corbyn even before his election.

The powers that be fear a Corbyn victory in the 2020 general election. More immediately, they fear the widening of a political debate that they’d long narrowed down to the minutiae of the system’s management.

“Capitalism needs all the parties it can get,” the deputy editor of the Tory Daily Telegraph observed during the leadership campaign, fretting that a Corbyn-helmed Labour Party would make debating public ownership or higher taxes respectable again. On a less elevated plane, an unidentified general reassured readers of Murdoch’s Sunday Times that the army would stop a Corbyn premiership by “fair means or foul.”

The establishment is hoping the right wing of the Labour Party will forestall the need to consider a Pinochet-style solution to the Corbyn problem. Unfortunately for them, the New Labour factions scarcely appear to be a coup-ready vehicle at the moment.

The mere fact of Corbyn’s election underlines the point. Though surprising, his path to victory was eased by the sheer inadequacy of the candidates arrayed against him, tedious career politicians scared of their own shadows and devoid of vision or passion. The most thoroughly Blairite of the bunch, Liz Kendall, heir to the legendary New Labour machine, won just 4.5 percent of the vote.

The Blairites’ underlying difficulty is not just their shortage of inspiring candidates for high office. It is their absence of any coherent message, never mind a compelling one, to suit the post-2008 world. One of the more honest of their ilk, MP Ivan Lewis, recently offered a peerless summary of the hurdles impeding their revival:

The spectre of Iraq. Being too starry-eyed about the private sector’s role in reforming public services . . . our approach to business and the market. On the one hand coming too late to the need for an active industrial strategy. On the other, refusing to embrace the need for serious dialogue with business about ethics as well as profits . . . insufficient concern and not having serious answers to widening inequality in the UK and across the world . . . the self-indulgent divide between “Blairites” and “Brownites” . . . the belief that only those who belong to a small elite usually connected to Tony and Gordon have a right to lead the Labour Party.

Any move against Corbyn will have to grapple with this legacy and put forward a credible forward-looking agenda.

A coup attempt is still not out of the question. But the aborting of party democracy by a right wing without plausible policies or presentable personalities clearly risks splitting the party from top to bottom.

If such an attempt did come to pass, the most effective preventative force would not be the Labour rule book — even if it does offer some strictures against removing an elected leader through backroom machinations — but the mass movements that brought Corbyn to power in the first place.

To maintain this mobilization, Corbyn and his supporters in the party leadership must deliver on their promises while also planning to fight and win an election against a Tory government and an internal Labour opposition doing everything possible to tilt the playing field.

These are all real challenges to the existing left, but they are worthwhile ones. Can a fighting alliance between the most energetic of the new movements against imperialism and capitalist globalization and the sturdiest organizations of the labor movement create a new opening to overturn the ruling elite and build a socialist society? Though the answer is unclear, the question seems the only one worth asking right now.