Say what you like about Boris Johnson, he can always be relied on to let you down. He is a serial liar who is trusted least by those who know him best. He is also an industrial-strength incompetent whose parliamentary supporters include just one of the ministers who served with him during his rackety two years as foreign secretary. Then there is the hefty back catalogue of offensive remarks and a private life that would stagger David Lloyd George or the Duke of Wellington. Rory Stewart, one of the other competitors in the leadership race, has even suggested that Mr Johnson isn’t fit to give proper instructions to the commanders of Britain’s nuclear submarines. Not safe with the deterrent is an accusation that Tories sometimes level at Labour leaders, but I’ve never before heard it hurled at a putative Conservative leader by a fellow blue.

This is a short summary of reasons that other Tories supply to explain why prime minister Johnson is a reckless idea. You hear them often from Tories who are nevertheless voting to install him at Number 10. Written off as a busted flush by many colleagues just a few months ago, the boy who once talked about becoming “king of the world” is closer than ever to capturing the premiership of Britain. If all is not forgiven, it is at least being temporarily forgotten in a collective outbreak of double-think and blind desperation.

His expectations-beating performance in the first round of balloting pulled in more votes from Conservative MPs than the next three contenders combined. This makes it impossible for rivals to keep him out of the final run-off unless he self-destructs. Might he? The cliche of his campaign is “the only person who can beat Boris is Boris”, which is why his team have strictly rationed the media appearances of a man who usually gorges on publicity. Colleagues enjoy conjecturing what could possibly now derail a man who has miraculously survived so much previous scandal. “Another love child falling out of the cupboard wouldn’t do it,” suggests one Tory MP of many years standing. “With Boris, all that is already in the price.”

One of his career hallmarks is a capacity to bounce back from episodes that would have been terminal for other politicians. His fellow Tories think that something seismically scandalous – probably something to do with money – would have to be revealed to prevent him from making the final two.

Watchers from abroad are looking on with incredulity, but there is a sort of rational explanation for his success. One component of it is the widespread feeling among Tory MPs that their next leader has to be someone who campaigned for Brexit. This belief is not just confined to Leave-supporting Tory MPs. A lot of those who were Remainers think this as well. After the May experience, another Remainer as leader won’t do, nor will a born-again Brexiter. This helps to explain why Jeremy Hunt, a very distant second in the first ballot, has not attracted as much support as he expected. The belief is that only a Brexiter stands any chance of selling a compromise to the party without being called a traitor to the cause. Another reason for thinking that the next Tory prime minister has to be a Brexiter is that putting one of them in charge is the only way for Brexiter fantasies to be tested to their final and irrefutable destruction.

Mr Johnson’s campaign is much slicker than the shambolic effort of three years ago. His leadership team includes Gavin Williamson, who was a senior figure on Theresa May’s winning campaign in 2016, and Andrew Mitchell, who was a senior figure on David Davis’s losing campaign in 2005. Between these two former chief whips, they know both what to avoid and what to do in order to win.

He has been further helped to a commanding early advantage by the state of the competition. Among non-Tories, Mr Stewart’s attention-seizing and guerrilla-like campaign has made him the break-out star of the battle. Unfortunately for him, this is a contest in which non-Tories have precisely zero votes. Mr Hunt is failing to erase the perception that he is a smoother, blander version of Mrs May in a competition where it pays to be as different seeming to the outgoing prime minister as possible. Historically, successful leaders are often those who can fuse a compelling personal story with a narrative about spreading opportunity. Sajid Javid is trying to serve this recipe, but it’s not pleasing the palate of enough of the diners he has to impress. Dominic Raab has tried too hard to be the macho man for the Brexit ultras. He unnerved even some of them by saying that he might attempt to shutter parliament in order to ram through a no-deal Brexit. This is supposed to be a contest for the prime ministership of a mature democracy, not the chairmanship of the junta in a banana republic. Michael Gove is still struggling to recover his balance and answer the charges of hypocrisy after being compelled to admit that he has snorted mind-bending narcotics other than Brexit.

In these contests, momentum tends to be self-feeding. When a bandwagon is rolling, the careerist seeks to clamber aboard while seats are still available. The Johnson team is telling wavering Conservative MPs that they should leap on the bandwagon before they are run over by it. I’ve heard all sorts of explanations from Tories about why they are swallowing their misgivings and voting for the former foreign secretary, including one MP who revealed that his wife and children are threatening to punish him by changing the locks to the family home. Whatever the surface reasoning, it often boils down to the hope of wedging their bottoms into the back seat of a better class of government limo.

Farage is a giant magnet attracting clouds of iron filings in the direction of the former foreign secretary

His big lead and the close bunching of the also-rans ought to be an advantage to the frontrunner in this week’s sequence of elimination ballots. The energies of the following pack will be concentrated not on attacking him, but wrestling with each other to be the second name that will be put to Tory members. The climactic parliamentary phase may well involve some of the chicanery for which Tory leadership contests are renowned. My conversations with Tories suggest that Mr Gove is the rival most feared by the Johnson camp. No one knows the other man’s vulnerable spots better than the fellow Brexiter who destroyed the last Johnsonian leadership bid with a last-minute betrayal. His team don’t fancy a Johnson-Gove cage fight and would prefer the other finalist to be Mr Hunt. They may be able to contrive this outcome by telling some Johnson supporters to switch behind Hunt to ensure that he beats Gove in the last stages of the parliamentary balloting.

He wouldn’t be winning without the willingness of many Tory MPs to suspend their disbelief. They are working terrifically hard to persuade themselves that they will get the version of Boris Johnson that they like without any of the features that repel them. So he’s getting the backing of Brexit ultras who claim he’ll deliver their version of the enterprise. He’s also garnered support from one-nation-type Tories who are telling themselves that the former mayor of London is really a liberal centrist. This coalition is riddled with ideological contradictions and he has already made promises that he simply won’t be able to fulfil. Don’t imagine that Tory MPs aren’t aware of this. The sentient ones are perfectly conscious of it as they equally know that he is a wild gamble that could go disastrously wrong for both their party and their country.

Fear is the key to understanding why, fear most of all of Nigel Farage. This is the single most important factor propelling Boris Johnson towards Number 10. The leader of the Brexit party is not on the ballot paper, but he is the most influential personality in this contest. He is a giant magnet attracting clouds of iron filings in the direction of the former foreign secretary. By far and away his biggest-selling proposition to Tory MPs terrified of losing their seats is that he is the only one of them with the force of personality to stand any chance of suffocating the Brexit party and defeating Labour.

And if it all goes horribly wrong? At least, I often hear Tories muse, a Johnson premiership “will cheer everyone up”. When your party looks like it is going to hell in a handcart, they reckon you might as well hurtle towards the inferno with a smile on your face. I warn them not to repeat this in public because I am not convinced that the wider nation will be laughing with them.

• Andrew Rawnsley is Chief Political Commentator of the Observer