Right-wing Democrats’ claim that the party’s left lost it votes to Donald Trump exposes the same fixation with obsolete conceptions of the “centre ground” that dominates right-wing Labour thinking. Politics is conceived of in a linear fashion in which the party closest to the middle wins.

That model is not applicable to an era of crisis, as Ocasio-Cortez points out. There is no evidence that endorsements from “moderate” Republicans such as former Ohio governor John Kasich helped the Democrats: in fact, in Ohio, Trump’s majority increased. By contrast, “every single candidate that co-sponsored Medicare for All in a swing district kept their seat. We also know that co-sponsoring the Green New Deal was not a sinker ...”

The known transfer of voters from Bernie Sanders to Trump illustrates the real Democrat weakness: being seen as the Establishment option. The Democrats clinched the presidency despite that, precisely because of the passion and anger of their left and the impact of mass movements such as Black Lives Matter on the political scene.

In the same vein, Labour surged despite its MPs in 2017 because of the grassroots organising of Momentum and a mass-rally campaign that made it look like the insurgent force in politics. And it sank in 2019 when the party’s obvious hostility to implementing the result of a UK-wide referendum allowed Boris Johnson to paint it as the Establishment.

So much is history. But the position and priorities of the left now must draw on it.

Causes championed by left-wing Democrats such as the $15-an-hour minimum wage and the Green New Deal remain popular, just as polls have consistently shown Labour’s bolder manifesto policies - its own Green New Deal, extending public ownership, kicking the privateers out of the NHS — to be popular too.

The Joe Biden administration is unlikely to move on them. It faces a Republican-controlled Senate that has the power to veto legislation. Even on foreign policy, where presidents have greater freedom of manoeuvre, Biden’s power is limited. He can rejoin the Paris Agreement on climate change; he cannot force a Republican Senate to pass laws that would actually reduce emissions.

Real as these obstacles are, they will also be excuses. The right will push the left to accept that its causes are impossible under current circumstances and not to campaign on them; but it will be happy to do so, since it objects to most of these policies anyway.

The only way to advance the left agenda that people and planet desperately need is outside official political channels - through mass campaigning that places pressure on office-holders to act. In the US this has the added advantage that a militant left is more likely to win the two Georgia Senate run-offs next year, the party’s only hope of ending Republican control and being able to seriously legislate at all.

The circumstances here are different, but the conclusion must be the same.

Labour’s leadership will not press willingly for the radical changes we need: a zero-Covid strategy, as called for by the People’s Assembly; the nationalisation of stricken industries and investment in a green industrial revolution to protect and create jobs while meeting the climate-change challenge; an end to privatisation and outsourcing in our public services.

But the appetite for all this exists - and it can be won, if sufficient pressure is built up from below. Government U-turns over school reopening in the summer over exams, over evictions, over extending furlough, have been the result of public protest and trade-union organising. Not one has been a response to pressure from the official opposition.

The real opposition in this country is no longer parliamentary. It needs to develop strategies to force change despite that.