THE long-expected calamity has come to pass: Boris Johnson has been chosen as Britain’s Prime Minister.

In his victory speech Johnson named three priorities: to “deliver Brexit, unite the country and defeat Jeremy Corbyn.”

On the vital importance of the last, the incoming and outgoing prime ministers were in complete agreement: congratulating her former foreign secretary, Theresa May tweeted that he could count on her support to “keep Jeremy Corbyn out of office.”

Britain’s Establishment remains terrified of a Corbyn-led government and what little unity it has left is summoned up to try to exorcise this spectre.

The Tory Party has given that job to Johnson. He will be a dangerous opponent.

Criticism of Johnson tends to focus on his personal “unfitness for office.” Johnson is clearly a repulsive character and his record of race-baiting, dishonesty, reckless risk-taking and egotism will make him a terrible prime minister.

But the labour movement has a duty to assess political risks based on class politics rather than personalities.

May was the author of the “Go Home or Face Arrest Vans” under the Conservative-Liberal Democrat administration of 2010-15 and as PM presided over the Windrush scandal that saw black British citizens deported and denied medical treatment.

David Cameron conjured up images of a “swarm” of migrants — actually refugees fleeing wars which his government helped to ignite, as with its catastrophic assault on Libya. Johnson is not the first PM with a racism problem.

Where his coronation both poses a risk and presents an opportunity to the left is in his greater distance from the Establishment “mainstream” and the already evident breach between him and parts of the permanent state.

Britain remains mired in one of the most serious political crises in its history. The ruling class has largely lost its legitimacy and governing institutions are held in deep contempt.

A popular vote to leave the EU upset decades of Westminster consensus and has spawned what could still prove a terminal crisis for a Tory Party whose membership are gung-ho for a policy its big finance, fossil fuel and hedge-fund paymasters regard as madness.

The crisis stretches way beyond our borders. It stems from the current economic set-up’s delivery of worsening jobs and living standards, growing poverty and joblessness and patent inability to address systemic problems.

We see it in Matteo Salvini’s brutal war on refugees in the Mediterranean and in Emmanuel Macron’s savage repression of mass “gilets jaunes” protests in France.

But Johnson’s playbook is the US one and like Donald Trump he intends to mobilise intolerance and fear as weapons against a resurgent socialist left that — unlike the right — could actually resolve the crisis in the interests of ordinary people.

We have only to look at the US crowds chanting: “Send her back” about a black Minnesota congresswoman to see how frightening the future Johnson represents could be.

At the same time, one of the strengths of the Corbyn-led left has been its ability to speak to parts of the country politicians have long ignored, providing the novel spectacle of mass Labour Party rallies even in old Tory strongholds like Canterbury or Cornwall.

Johnson poses a particular threat to black and Muslim communities and the left needs to draw on the strength of these communities in building a fightback rooted at local level.

Johnson epitomises upper-class contempt for working people and the left can, if it stands with and for working people and refuses to patronise them, show that it has answers that he doesn’t.

To do so we must build a fighting left movement that clearly offers sweeping, radical change and appeals to the angry, the wronged and the destitute.

If we fall into the trap of alliance with the “status quo” wing of the Establishment for fear of Johnson making things worse, we will dig our political graves.