Mathieu Kassovitz’s 1995 epic La Haine, tracing the lives of disenfranchised youth in the Parisian slums, begins with the story of a man falling from a great height. “So far, so good; so far, so good; so far, so good,” the narrator assures himself. Then the screen is engulfed in flames. “It’s not the fall that matters,” we are told, “it’s the landing.”

At times in the past five years, the Left has scaled great heights. So much so, in fact, that a socialist Labour government seemed visible on the horizon. There were many achievements along the way – from overturning an austerity consensus that held total sway over British politics for years, to remaking Labour as a mass party with more than half a million members. Thirteen million people voted for a decisive break with neoliberalism in 2017; and ten million voted for a radical left-wing manifesto in December. More than had backed Miliband, Brown — even the last Blair government.

But the general election defeat was, nonetheless, severe. It has chastened the Left and this newfound timidity was evident in Rebecca Long-Bailey’s leadership campaign. It suffered from many of the weaknesses of Corbynism. It was, in fact, born into the inertia that a lack of succession planning produced. Unfortunately, it had few of Corbynism’s strengths – and could not inspire the kind of movement necessary to beat the odds.

Keir Starmer deserves congratulations for his victory. He stood on a platform of making at least some of the radical policies of recent years electable. It remains to be seen how durable his leftward commitments will be once they come under pressure from the media or the right-wing of the Parliamentary Labour Party. Regardless, there will no longer be a socialist as Labour leader – Starmer is a moderate figure and not one whose politics will threaten the wealthy or powerful.

For the Left, this cascade of defeats makes clear that we are in a fall. Today’s results suggest that we have not reached terminal velocity. In the past, the Left has responded to these moments with the bitterness and recrimination of a movement whose hopes of changing the world were dashed. It has fractured and fragmented and given in to internecine factionalism. It has guaranteed, in other words, that its defeats were not temporary but generational.

That does not need to be the case this time. Corbyn’s leadership of the Labour Party revived socialism in Britain. It made it possible to call capitalism itself into question – and have an audience for your argument. Perhaps most importantly, it convinced an emerging generation whose material circumstances disposed them to fundamental change that socialism could offer solutions to the problems in their lives.

The arguments for socialism have not gone away. The coronavirus crisis means we face the deepest recession since the 1930s. This weekend even the Financial Times was arguing that four decades of neoliberalism had to be discarded in response. Already, we had seen years of economic stagnation and growing inequality. The climate emergency and resurgent far-right threaten further disaster in the years to come. Capitalism does not have the answers to any of these great questions of our age.

The task for socialists now is to learn the lessons of defeat, organise and rebuild. But we can only do this if we are clear-eyed about the reasons for our progress in recent years. Before Corbynism, the socialist Left was truly marginal. It played important roles in movements against war and austerity – but it was disparate, divided between a weak Labour Left and various radical groups who counted their memberships in the dozens or hundreds at most. We must not return to those days.

Jeremy Corbyn’s leadership of the Labour Party brought socialist arguments back into mainstream politics for the first time since the conquest of neoliberalism in the 1980s. It is certainly true that, under Corbynism, extraparliamentary movements were not as strong as they needed to be. A return to the work of building those is necessary – but so is organising socialists through the Labour Party.

The sources of hope on the socialist Left in the past decade — from Syriza and Podemos to Corbyn and Bernie Sanders — have come through engagement in mass party politics. Before this, many years of focus on street movements and minoritarian radicalism had failed to grow our ranks or proliferate our ideas. Socialists should remember this, and stay in the Labour Party despite today’s disappointment.

As this economic crisis deepens, the case for class politics will grow. With each passing week the inequalities in our society will be brought into starker relief, as will the nature of our economic system and who it is designed to protect. Despite its gentrification in recent decades, Labour remains the political wing of the trade union movement – and the only party which can reasonably aspire to represent the working-class as a class.

That must be the Left’s anchor in the years to come. The great risk of Starmer’s leadership is that it finally completes Labour’s realignment away from a party based on uniting people across cultural divides on the basis of their class interests and towards one which unites people across class divides on the basis of liberal social views.

This would be a disastrous outcome for socialist politics in Britain, trapping us in a groundhog day of Brexit culture wars for a generation. And doing so at exactly the moment when systemic alternatives to capitalism will be needed most. The only way it can be avoided is for socialists to be active in the labour movement – rebuilding a Left within the Labour Party and renewing our unions, a focus which was absent all too often under Corbynism.

Today is a defeat for the Left. But the real victory for our opponents would be watching the forces we have amassed in recent years scatter to the wind. We cannot allow that to happen. The need for socialist politics is too urgent to give in to the temptation to wallow in self-pity. We have a responsibility to do better.

We are falling at the moment – the question now is how we land. That determines where the Left will be when we start climbing again.