When Boris Johnson became prime minister, I asked a European diplomat, a veteran of overseas missions, for help putting Britain’s political mess in perspective. Where, I asked, did we sit on the spectrum of international dysfunction? The diagnosis was mostly reassuring: a wobble not a nosedive. But there was one symptom of profound malaise – people contacting the embassy in search of an EU passport. In stable democracies, it is not normal to shop around for alternative citizenship as insurance against your home state turning rogue.

I have had those conversations – some half-joking, some deadly serious – with people activating dormant Irish ancestry or adopting the nationality of continental partners. I know couples, happily unmarried for years, who have tied the knot in order to expedite naturalisation or guarantee their children’s status as British and European. Before the referendum, that combination was available without government permission.

It should be easy to prescribe Labour as the antidote to the venom that Johnson injects into the body politic

And that is the most intimate and the least politically celebrated benefit of EU membership. It is freedom of movement expressed as the dissolution of interior borders: the assembly from individual lives of hybrid European families. The symbolic restoration of those borders was felt with brutal clarity the morning after the referendum. Inevitably, the symbolism acquired sinister bureaucratic expression: millions of European citizens had the presumption of a right to belong in Britain withdrawn. They had become aliens in the place they called home.

These are the people Johnson accuses of “treating the UK as though it’s part of their own country”. The rhetoric was efficiently insidious. In just a few words it cast EU nationals as an invasive horde abusing the hospitality of the indigenous population.

The divisive language, harking back to the uglier themes of the referendum campaign, hints at fraying nerves in Conservative HQ. Yanking the anti-immigration lever is a sure sign of impatience with an electorate that has proved less responsive to the prime minister’s charm than Tory strategists hoped. That alleged charm is a veneer that cracks and flakes in the sustained heat of a campaign, exposing a coarse grain of nastiness underneath. It was visible this week to all who saw Johnson on TV holding his gaze stubbornly aloft to avoid looking at a photograph of a sick child asleep on a hospital floor.

Many Tories know well enough that the main requirement for liking Johnson is ignorance of his true character. The more he is exposed, the wider grows the gap between mask and man. His amiable act works in short bursts in front of receptive audiences. Too long in the limelight and he struggles to stay in role. Not only does he lack decency and compassion, but he cannot even fake them.

Boris Johnson during an interview with ITV, in which he refused to look at a photograph of a sick boy on a hospital floor. Photograph: ITV

At this point in the argument, it should be easy to prescribe Labour as the antidote to the venom that Johnson injects into the body politic: the cloying mix of xenophobia, deceit, entitlement and faux bonhomie. But many of the hearts that sink at the prospect of a Tory triumph on Thursday cannot quicken with joy at the thought of Jeremy Corbyn being prime minister instead. Mine is one of those hearts. It will not beat in time with the Labour campaign in much the same way that it will not be reconciled to Brexit. There is the same chilling feeling of a border that was not there a few years ago, cutting across the intimate terrain of identity. It is the line, drawn by Corbyn, which many Jews feel they cannot cross.

Plenty of Labour supporters (and non-aligned remainers) are weary of this topic. I have seen eyes roll because it is unhelpful to point out the awkward facts about the only anti-Tory candidate for prime minister: that Corbyn has been a comrade to antisemites, Holocaust deniers and people who celebrate violence against Jews; that the claim to oppose all forms of racism rings hollow from a man who saw nothing offensive in a mural depicting caricatured Jews playing Monopoly on the backs of bowed bodies. This is the man who once dismissed “Zionists” for failure to “understand English irony”: despite “having lived in this country a long time, probably all their lives”. Corbyn was the magnet to Labour for Jew-hating cranks and conspiracy theorists who bullied two Jewish MPs out of the party. His peevish, reluctant apology contains no trace of understanding or real contrition.

None of that diminishes Johnson’s prolific record of racially aggravated offences. Outrage does not have to be rationed for one side or the other. Reluctance to see Corbyn in No 10 does not use up a portion of horror that could otherwise be spent on Tories. Both sentiments can coexist. But the intensity of my desire to see Johnson beaten can also fuel my anger that Labour demands support for Corbyn as the means to do it.

Johnson’s nationalist train, driven by locomotive mendacity, can be derailed only by a barricade of opposition MPs. There are feasible configurations of a hung parliament with a sufficient number of Liberal Democrats and independents to make a change of leader the condition of buttressing a Labour-led administration. It is just about possible, for one day more at least, to imagine a Britain that is spared the lunacy of Brexit, and a Labour party no longer in thrall to Corbyn. But the combination defies electoral probability. Those of us who wish for it must be reconciled to a darker prospect. We live with the undertow of sadness and dread. We are braced for that feeling, like seeing callous hands rummaging in a private drawer where a delicate, tangled identity is stored and pulling at the threads. It feels like exile.

• Rafael Behr is a Guardian columnist