Even if the PM were to offer to quit tomorrow, she would not not win her vote.
Because for the True Brexit believers of the European Research Group, the backstop is more important than who occupies Number 10.
They have been sounded out by ministers about whether they would back the PM’s reworked Brexit deal, if Theresa May were to offer herself up in ritual sacrifice.
They have rejected her martyrdom. Partly because they are sure it will happen come what may.
But more importantly because they fear that even if one of their own - a Raab, Johnson or Davis - succeeded May, it would be impossible to cancel the backstop.
And annulling the backstop is more important - for them - than determining who occupies Number 10.
One of their number told me that even if a “proper” Brexiter became PM in short order - and they are by no means confident of that - they simply don’t see how they would ever get out of the backstop, short of reneging on the Withdrawal Agreement AFTER it has been ratified.
"We are not in the business of ripping up international treaties," he said. "We’ve thought about it but it is not a good look for this country."
So burying the backstop is all that matters to them.
And what that motivates the ERG to do is to ensure both that the PM loses the meaningful vote tomorrow - which ministers expect her to do by a margin of well over 100 votes - and then that Parliament does not eliminate the option of a no-deal Brexit in any binding and permanent way.
I will elaborate on this soon, but my own central projection has not changed - that even if MPs seize some control of the Brexit agenda, as per the manoeuvering by the three-headed backbench beast known as Letwin-Cooper-Boles, we are heading for a no-deal Brexit, though more likely at the end of June than the end of March.
And for what it’s worth, when I put this to members of the Cabinet, no one seriously demurs - though few actively want that outcome.
Arguably we are witnessing the greatest diplomatic humiliation for a British government in more than half a century, and our political system seems powerless to prevent it.