Team Boris have always operated on the theory that the only person who could beat Boris Johnson in the Tory leadership contest was Boris Johnson himself. After the events of the past few days it's just possible that their worst fears may be realised.

For months the campaign team behind Johnson had run a very slick, very controlled operation. They knew their man was popular with the 150,000 Conservative members who would determine which of the final two candidates became the next prime minister and so devoted all their energies to wooing the 312 other Tory MPs who would get to decide on the eventual shortlist. In the process, Johnson was kept on a strict leash. Breaking the habit of a lifetime, Boris made almost no public appearances – instead sending out a praetorian guard of trusted lieutenants to speak to the media on his behalf – in case he screwed up.

It was a strategy that worked far better than Team Boris had dared hope. By promising different things to different people – not just alternative visions of Brexit but jobs too – he was able to win over the majority of the hardline Eurosceptics of the European Research Group as well as the more moderate wing of the party who wanted to avoid a no deal at all costs. Tory MPs always seemed to come out of a meeting with Boris having heard exactly what they wanted to hear. The ERG were convinced the UK would be leaving the EU on 31 October come hell or high water; others felt there was wiggle room and that Boris would never leave without a deal.

The stars even appeared to further align for Johnson when the European elections returned the Brexit Party as the overall winner. This spooked the entire Conservative Party who feared they would be out of office in any general election and opinion polls suggested that Boris Johnson was the only person who stood a chance of leading the party into a fourth term of office. Come the first round of voting in the leadership contest, Johnson was so far ahead of all his rivals that his place in the final two was guaranteed.

The simple fact of the matter is that the behaviour and character of the man who is likely to be the next prime minister is quite clearly a matter of public interest

So much so that his team were able to manipulate who made it into the final round against him. First his supporters lent votes to Rory Stewart to eliminate Dominic Raab, the only other candidate who was offering a No Deal Brexit. Then the votes switched to Sajid Javid to knock out Stewart, whose straight-talking campaign style might have exposed Johnson's natural bluster. And for the coup de grâce, his team bolstered Jeremy Hunt's tally to get rid of Michael Gove. A piece of electoral chicanery that was doubly sweet for Johnson. Not only was Hunt looked on as the continuity, Remainer-lite candidate who the Tory members would not tolerate, it was the perfect revenge on Gove, who had undermined Boris' previous leadership bid in 2016.

All seemed set for a coronation march as Johnson and Hunt began their 16 hustings of Tory members around the country. Then came the late night argument at the Camberwell flat with Johnson's partner, Carrie Symonds. An argument that was so loud and so prolonged, in which plates and glasses were smashed, that it disturbed several sets of neighbours who called the police and recorded the shouting in case it was needed as evidence.

Some details are known. Symonds was heard shouting “Get off me,” “Get out of my flat” and “You're spoiled. You don't care about anything.” Boris yelled, “Get off my laptop.” The police did come and concluded that there was no need for any action. But that still leaves a lot of questions unanswered. This was clearly no everyday lovers' tiff. We all have arguments, but very few have ones that sound so threatening that neighbours call the police because they are concerned for the safety of one or both of the couple. And then there's the curious detail that the police twice lied to the Guardian, who had been passed a recording of some of the incident by one of the neighbours, by denying they had ever been called out to the Camberwell flat.

Friends and supporters of Johnson have tried to make the neighbours the villains of the piece, suggesting that the decision to make the recording public was politically motivated. The neighbours' crime had been to vote Remain in the referendum. It can't be long before some people are going to denounce Dominic Grieve as a dangerous Trot. But the simple fact of the matter is that the behaviour and character of the man who is likely to be the next prime minister is quite clearly a matter of public interest.

If character is your main selling point, then it's only fair that character is examined

Team Boris simply can't wish that away. Their central dilemma is this. The whole pitch behind Johnson's leadership bid is that the serious politicians have failed to deliver Brexit and that only he has the necessary strength of personality to get the job done. If character is your main selling point, then it's only fair that character is examined. Johnson is known for being serially unfaithful to his partner, for telling lies as and when it suits him, for having a poor grasp of detail and for having a volcanic temper when he doesn't get his own way. Are these really the character traits the UK is looking for in its next prime minister?

At last Saturday's first hustings in Birmingham, the interviewer, Iain Dale, asked Johnson to explain exactly what had taken place in the early hours of Friday morning. Johnson declined to answer, saying he didn't think people were very interested. Some Boris loyalists in the audience seemed to agree and booed Dale. But then a recent YouGov poll has found that many Tory members would also be prepared to wreck the economy, to break up the Union and to have Nigel Farage as leader just to deliver Brexit: not necessarily a fair representation of the country Johnson aspires to lead.

Johnson's refusal to answer was a huge misjudgment. Not only did it make him look evasive, it ensured that the questions over his character would only get more insistent over the coming days and weeks. His inability to say what happened between him and his partner makes many people believe that the incident was more than a run of the mill tiff. After all, many domestic arguments to which the police get called out do end up in violence, with the victim – usually a woman – injured or worse. Three days on and Boris has still not been able to provide an explanation for what happened and by now it's too late. The question marks over his campaign will hang over the rest of the leadership campaign. If he can't be trusted to behave decently towards his girlfriend, how can he be trusted to run the country?

The problems for Johnson don't end there. He might want to move the debate on to his political record, but even that doesn't stand up to scrutiny. His time as foreign secretary was an unmitigated disaster. He managed to endanger the British national Nazanin Zaghari-Ratcliffe, who was being held in an Iranian jail. He caused diplomatic tensions on various overseas trips and foreign office officials despaired of him. Johnson likes to talk up his record as London mayor, but even that doesn't bear much scrutiny. He left a whole load of broken promises and wasted money on vanity projects in his wake. Then there's the casual racism – women in burqas compared to letter boxes and references to “piccaninnies with watermelon smiles” – that he tried to brush off as a joke. Just Boris being Boris.

Nor is he any clearer on Brexit – the one thing for which Tory MPs and members are supposedly prepared to overlook all his other shortcomings. It's not clear if he's determined for the the UK to leave the EU on 31 October or whether he thinks it's just “eminently feasible”. Nor can he explain how he's going to do it. Rather he just talks in faux-Churchillian rhetoric about the country “testing its mettle”. He doesn't even seem to understand the basic point that without a deal there is no implementation period.

All of this rather plays into the hands of Hunt. The odds on the rank outsider are shortening by the day. Johnson may still be a firm favourite but the coronation is no longer necessarily a done deal. The more exposure he gets, the more the doubts about his ability set in. Team Boris was right all along. The one man who can beat Boris is Boris himself. It's possible the UK's version of Donald Trump will get away with it, just as the US president has so far done. But never underestimate the capacity of a narcissist to self destruct.

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