There is no crisis at Westminster so serious that it cannot be made to look trivial by the inclusion of Boris Johnson. And there is no scandal involving Johnson that cannot be explained, partially or wholly, by his lies. Those are axioms of post-Brexit politics. The House of Commons committee of privileges is due to publish a report concluding that a former prime minister turned his back on truth and put himself in contempt of parliament. The gravity of the offence invites a serious discussion about the safeguards in British democracy. Or it should. Johnson lied because he had broken the rules that most other people observed during the pandemic, often at significant personal cost. He lied because he felt no duty of submission to rules imposed by his own government or any other authority. He lied because breaking rules and refusing to admit it had been a reliable method of self-advancement throughout his life, propelling him all the way to Downing Street. He lied because that is what he does. Those facts being established, and Johnson having quit the Commons to avoid the indignity of a suspension, the main question left hanging is how such a man ever reached a position of power for which he was obviously unfit. What sickness in British politics produced the hallucination of merit in Johnson’s candidacy for No 10? The question presupposes that the fever has broken. Sweaty feuding between supporters of the former prime minister and the incumbent, once Johnson’s protege, suggests otherwise. The row with Rishi Sunak is ostensibly about something other than lockdown breaches, but they are connected in the way that multiple items of garbage can burn separately in the same skip fire. Sunak is accused of vetoing honours that Johnson was entitled to dole out on his resignation as prime minister, and of reneging on specific assurances that some MPs would get their peerages in due course. Downing Street says that is untrue. Nadine Dorries, one of the thwarted nominees, decries a snobbish conspiracy by rich kids in No 10 to prevent a working-class girl from Liverpool achieving the ladyship that Johnson had said was in the bag. Another explanation would be that Johnson lied. This is the trivialising process in action. Somehow debate lurched from the constitutional principle that MPs be accountable for the veracity of what is said in parliament to playground recrimination between rival gang leaders and their mates. The same manoeuvre skips glibly from a public health emergency in which hundreds of thousands of people died to bickering over the timetable on which failed ministers should be allowed to swap a seat in the Commons for a cushier berth in the Lords; all against the backdrop of a brutal cost of living crisis. Johnson is not responsible for all that is absurd in Westminster. The whole business of leaders draping their cronies in ermine was grotesque before he made it obscene. But his turpitude is radioactive. It illuminates flaws in a constitutional order based on protocols and propriety, while accelerating its decay. The more British democracy has been exposed to him, the less serious it has become. His toxic self-involvement has contaminated the Conservative party so completely that even in rejecting him it inflates his vanity. He is a lump of weapons-grade narcissium polluting the political air. Enough Tories have diagnosed that problem to want rid of him, although that urge is reversible. Less than a year ago Johnson was defenestrated by the parliamentary party. Only a few months later, a hundred MPs were ready to nominate him as the best person to replace Liz Truss. Back in the summer of 2019, when Theresa May resigned, plenty of Conservatives swore sacred oaths to prevent Johnson ever reaching No 10, before endorsing him and serving in his government. That was the Rubicon moment. Crossing to Johnson’s side required wilful rejection of any attempt to enact Brexit while remaining in some way cognisant of economic and diplomatic reality. May had burned herself out trying to reconcile ideological demands for complete rupture from Europe with rational mitigation of the cost. It couldn’t be done. Johnson represented the view that there was no real cost, only sabotage by enemies. And they could be overcome by a surge in national spirit, incarnated in a heroic leader – the archetypal offer of populism. Johnson’s great helmsmanship and Brexit as a dream of national renaissance are still fused in some Tory imaginations. He addressed that constituency directly in a resignation statement that cast the privileges committee as a “kangaroo court” installed as part of a plot “to take revenge for Brexit and ultimately to reverse the 2016 referendum”. The form and tone of the argument are cribbed from the Donald Trump playbook: self-pitying, paranoid, designed to stir bellicose nationalist grievance. The imitation would be more alarming if it wasn’t also desperate. There is an audience for the embittered Brexit betrayal myth, but not an election-winning majority. Its indulgence by Conservatives indicates a party already settling into opposition and, while US Republican-style derangement is an obvious trajectory once the burden of government is cast off, a restoration of beleaguered liberal Tory traditions is also available. For all the damage that Johnson has done, his power to make everything trivial has proved self-diminishing. He thought he stood above the institutions that he corrupted, but he was brought down by conventional democratic mechanisms. His lies about lockdown parties were exposed by a free press and punished by parliament. The Tory majority he claims as proof of his unique popularity did not save him. The system that swallowed his shtick also disgorged him. The real tragedy is that he was host to a more stubborn parasitic worm of an idea – the Brexit delusion that has nested in the guts of British politics and will not so easily be excreted. Rafael Behr is a Guardian columnist