Boris Johnson is a cheat and a liar; we all know this, it is priced in. Even those who like him know it – they just see it as roguish and charming that he can slide away from the consequences most of us would face if we had his behaviour. To trust him at his word is unwise. In any case, his deal is a bad deal by any measure of leftism: it points toward an exit where the good aspects of EU law would be shunned. An exit that is likely to leave the country much poorer, and one which will take away the vital right to freedom of movement. There are no last-minute bids to bring more Labour MPs onside, like the ones Theresa May feebly attempted once she had faced up to her lack of power; this is a deal for the Tory party, and a hard right Tory party at that.

Yet this is not why Boris Johnson should lose the vote on Saturday. There are honourable reasons to want to leave the EU, which exists currently as the worst version of a good thing; it is opaque, intransigent and at its worst, callous with human life. There are even good reasons to want to honour Brexit. Yes, it was a nasty, xenophobic campaign, led by the worst of instincts toward immigration and ideas of “freedom” which somehow amount to the freedom for workers to lose their rights. Nevertheless, it was a decision taken by the people. There is a mandate for its implementation. If you are a Labour MP in a majority-Leave seat, it makes sense to try to do your best to honour that commitment. But the theory that passing the deal might be part of a much-needed healing process for the country clashes with the reality that the fortunes of this deal and Boris Johnson’s success are inextricably linked.

Should the Prime Minister pass the deal tomorrow, he might not win an election immediately, but it will mean that he will have done what had been said to be impossible. This is the crucial fact. Boris Johnson must fail, and he must fail humiliatingly. Not because he is a liar, which he is. Not because his deal is bad, which is also true. He must fail because of what his success implies.

There are moments in which a country is lost; its structures still exist, the name is still there, and life carries on as before, but something in the idea of how it chooses to be is gone forever. So it was when Trump mocked a disabled journalist in front of a crowd, and was later elected president. So it was again when Bolsonaro humiliated former President Dilma Rousseff by praising her torturer to her face, and was later elected president. Boris Johnson mocking Paula Sherriff as she invoked the memory of Jo Cox was another such moment. Any support for him, for his political project, is support for that moment and what it represented.

Boris Johnson must fail. He must be associated with catastrophic failure.. He must be a cautionary tale for everyone else. Should he pass this deal, he will have one huge success (two, if you count the 2016 vote) to point to for the rest of his life. Even if we don’t fear the man himself, we should fear his followers; if this project isn’t defeated now, someone else will come and be even more brutal. Boris must fail to pass a deal, to win an election, to win his own seat. There must be no encouragement for those who want to follow in his footsteps.

Forget threats of deselection, the anger of the London liberal bubble, the gruelling task of going through Brexit for three more months as other problems pile up in the country and the world, the prospect of a vicious election in the bleak midwinter. These matter less. Remember this one crucial fact about Boris Johnson: when someone showed sincere fear for their very life, and brought up the violent death of one of their friends, he scoffed. This is the man that a vote on Saturday will empower; this is the man that will get to have at least one success against his name in the history books. Every moment that Boris Johnson stays in power is a moment in which the country becomes more like him. We might need to leave the EU, eventually, but not on his terms. Boris Johnson must fail.