Which is not to say he will succeed her as Tory leader and prime minister.
He may be the favourite to do so, but - as Sunder Katwala has pointed out - only once in the past half century has the initial frontrunner actually seized the Tory crown. Boris could yet blow it.
But his manoeuvres with his backbench colleagues have made it impossible for the PM to have her Brexit plan approved - were she to put her Withdrawal Agreement Bill to a vote, as she still promises to do - because he has persuaded them there is an escape from the Brexit deadlock that is destroying their party but not while she is in 10 Downing Street.
This view that Boris Johnson has done for Theresa May is not confined to the Brexiter ultras of the ERG.
It has been put to me as uncontroversial and incontrovertible truth by senior members of the Cabinet whose Brexit credentials are at best moot.
"What Boris did was convince my colleagues that if he were PM, he could persuade Brussels to ditch the hated backstop," said one.
"Or rather that it is worth a go. And if he fails then it is full steam ahead to a no-deal Brexit, though with proper preparation".
On this narrative, May's fate was sealed on Tuesday when in her last big Brexit speech she refused to countenance any renegotiation of the backstop, the default mechanism for keeping open the border between Northern Ireland and the Republic that is hated by Northern Ireland's DUP and Brexiters and is written into the Withdrawal Agreement.
It is irrelevant whether May is right or wrong that trying to change the Withdrawal Agreement would be a fool's errand.
Johnson has persuaded enough Tory MPs she is unreasonably defeatist and they have given up on her.
The way she refused to budge when MP after MP pressed her yesterday to end the investigation and prosecution of Northern Ireland army veterans also reinforced their view that she is permanently estranged from their values - even while the former attorney general, Dominic Grieve, said on my show last night that she is right and they are wrong, that it would be impossible to introduce a statute of limitations for soldiers that would not equally apply to terrorists.
It is no coincidence that Jonny Mercer, the Tory MP who has led the campaign on behalf of the retired soldiers, outed himself (again on my show) as an enthusiastic and important player in Team Boris.
His mission, he told me, is to persuade party and country that Johnson is the only leader for these critical times, that he is a One Nation unifier rather than the Trumpian sower of discord and mayhem many perceive him to be.
Grieve for one was wholly unconvinced, and signalled he could well vote to bring down a Johnson-led government, if that government were hellbent on a no-deal Brexit that Grieve sees as catastrophic.
By pure coincidence I also interviewed another Johnson acolyte on the programme, Jacob Rees-Mogg.
And what stuck me when talking with both Mogg and Mercer is quite how much preparatory work has been done to convert Johnson's legendary ambition into a key to the door of 10 Downing Street.
Their big and simple message is that the existential threat posed to the Tory Party by Nigel Farage and his Brexit Party is that the Tory Party itself has to reinvent itself as the true party of Brexit - and that would only be possible if they are led by their own populist demagogue for the social-media age, namely Johnson.
Which, as I said, is not to say that Johnson is a shoo-in as next Tory leader.
Politics is far too volatile and unpredictable for that kind of idiot's forecasts.
But just a glimpse at a way for Tories other than the May way is why minister after minister assured me yesterday that Theresa May would be gone soon (as I mentioned yesterday, they all think they know that she'll announce her departure timetable tomorrow - but when ministers speak to me about her, the sound is of whistling in the impenetrable dark).