Towards the end, Boris Johnson looked exhausted. He was a marathon runner staggering through the finishing tape, a boxer slumped against the ropes. Though perhaps that’s no surprise, judging by what the Covid inquiry had just heard about his woeful inability to focus forensically on the detail of policy or follow a scientific argument. Two whole days of being repeatedly confronted by evidence of his own inadequacies – plus accounts of his rage at having to shut down the economy just to save what he reportedly dismissed as old people “who will die anyway soon” – were always going to be a struggle, and yet he was still not the biggest loser from this unedifying episode. That would be his hapless successor Rishi Sunak. Whatever the Covid inquiry eventually concludes, Johnson can’t be sacked from anything much now. He has already lost his Westminster seat, and his new gigs – a £500,000 advance for his memoirs, plus a column for a newspaper that employed him knowing full well this was coming – cannot be taken from him by the electorate. The painful emotions stirred up by reliving it all have nowhere to go but towards an already wildly unpopular Conservative government, whose leader has become a lightning rod for anger and frustration over his predecessor’s broader legacy: not just the pandemic (though Sunak has yet to face his own grilling by the inquiry over that one), but the way nothing in Britain seems to work any more, and for the gradual realisation among leave voters that what they were promised will never be delivered. Having pitched himself as the man to clear up Johnson’s mess, Sunak is instead drowning in it. Which prime minister originally signed off on the idea of exporting asylum seekers to Rwanda, a plan that was always as unworkable as it is morally offensive, and which coincidentally unravelled just as Johnson took the witness stand? It was, of course, one Boris Johnson, who launched it the day after receiving his partygate fine in what was seen at the time as an attempt to deflect from his embarrassment. Sunak could have torn the Rwanda plan up on becoming leader but was too afraid of the Tory right, which has characteristically now turned on him anyway. Suella Braverman, of all people, is now publicly declaring the whole thing a sham; it’s as though the fable of the emperor with no clothes ended with the emperor herself gleefully announcing that she’s actually naked. Mortifyingly, it was Rwanda’s government that ultimately declined to sign any deal breaching international law, while the wilder fringes of British conservatism continue to demand one that does. Imagine being so bad at politics you cede the moral high ground to a dictatorship. No wonder Braverman openly fancies her chances, along with Robert Jenrick, the immigration minister who resigned this week, and whose rapid transition from Tory moderate (and longstanding Sunak friend) to champion of the headbanger tendency suggests a determination to be on the winning side. With the government seemingly too consumed by political infighting to actually govern, the Covid inquiry meanwhile reminds us how long it has been since anyone actually did. The overriding impression Johnson’s testimony left was one of a strange emptiness: a vacuum where leadership should have been in a crisis and now a foggy haze where insightful reflection is required. Whatever the merits of the Whitehall reforms Dominic Cummings suggested, at least he addressed the essay question posed by an inquiry expressly designed to extract lessons from the future. Pressed by the inquiry’s counsel, Hugo Keith KC, for his own suggested improvements, Johnson suggested hopefully that things would emerge as they went along. It was all too consistent with the picture Keith is building of a man fundamentally lacking in executive oversight or even much curiosity, confused by complex data and frequently just accepting the last thing he was told. The role of a prime minister presented with conflicting pieces of advice is to interrogate each and determine which is right, but we heard painfully little evidence of Johnson offering constructive challenge. The risk posed by “eat out to help out the virus”, the nickname government scientists apparently gave Sunak’s plan to woo the punters back into restaurants in 2020, was visible from space, but Johnson simply protested that nobody in the Treasury had put it to him that way: how was he to know more indoor socialising might be dangerous? He seemed galvanised only where the scientific consensus clashed with his own gut instincts, scrawling “bollocks” over a report on long Covid and resisting a second lockdown because – according to his chief scientific adviser’s diaries – he’d become “obsessed with older people accepting their fate”. (Though far from killing people who were on their way out anyway, research suggests that in the first year of the pandemic, the virus robbed over-75s of an average 6.5 years of life.) Time and again, confronted with awkward evidence of his private views, Johnson claimed he was merely playing devil’s advocate to test the argument. If so, he seemingly fooled his colleagues. Some critics have painted this inquiry as a waste of time, preoccupied with trivial gossip about who was rude to whom on the group chat. Johnson is indeed unlucky to have governed in the age of WhatsApp, which preserves the stuff people would never normally put on paper for posterity (with the exception, of course, of those messages mysteriously lost from Johnson’s mobile). But using them is a way of capturing something that often eludes inquiries, which is the unsanitised feeling of what it was actually like inside the room. No government gets everything right, but by focusing on whether Matt Hancock should have been sacked or exactly how the veteran cabinet secretary Mark Sedwill was eased out, this inquiry seems to be testing whether Johnson created an environment in which it was actively harder to make good decisions. That some Conservatives now want to install Braverman in his old role suggests a party utterly incapable of learning from experience. These are now clearly the last days of a dying government, and many will take comfort from that. But as the casual cruelty of the spousal visa arrangements announced this week confirm it is still capable of doing plenty of damage on the way out of the door, which is why Britain can’t wait until next spring or autumn for a general election. With Sunak loyalists now threatening privately to go to the country if his leadership is threatened, it is time both sides called each other’s bluff. Let the warring Tory factions, in time-honoured British fashion, take their fight outside. And give the rest of the country the fresh start we now so richly deserve. Gaby Hinsliff is a Guardian columnist