Before the big vote on Tuesday evening, the 27 EU Heads of Government will provide more reassurance – probably in the form of a collective letter to Theresa May, and in the context of the mandate confirmed in the last EU Council – that the controversial arrest of Northern Ireland
What does it mean?
Well, for those MPs who agonize about the opportunity or not to support the Prime Minister's Brexit plan and think that the word of political leaders is worth something, some votes may move in the direction of Theresa May.
And perhaps, in the words of a senior British minister, May will be able to frame the letter as both "substantial" and "legally" significant.
But it will not affect most of its critics, because the so-called Revocation Agreement will not be reopened and, whatever the legal strength of the letter, it could not exceed the international treaty that is the Withdrawal Agreement, so it will not there will be no legally binding guarantee.
This means that the PM continues to lose Tuesday night, but probably with fewer votes than it otherwise would have been.
These last minutes of maneuver highlight the single most important May mistake: his inability to build a majority in parliament for a vision of future UK relations with the EU.
If we knew what kind of business and security relationship we would eventually have with the EU, the backstop would not be the problem is true: there would be widespread trust on both sides of the channel that if the backstop was used , would be of a desperately short duration, for the simple reason that there would be a high degree of certainty about the post-Brexit negotiations to put in place alternative trade agreements that would make the seabed completely redundant.
But as stated by a senior EU government official, "given the principles and red lines on both sides, it is hard to see what future relationship we could ever agree".
Here's why it's NOT barking mad to suggest that the anti-return could remain in effect until after we're pushing all the daisies.
If only May had spent more ̵
But Jeremy Corbyn's vision of a post-Brexit relationship with the EU is a million miles from that of many of his MPs and that of Remainer Tory MPs and even further from that of MEPs. Brexiter Tory.
The one thing that unites most of them is their disdain for the backstop. That's why I can not find any minister who thinks there's a way to win on Tuesday.
What follows from the humiliation of that defeat?
Well, Foreign Secretary Jeremy Hunt is likely to correct the fact that Parliament finds a way to block a Brexit without agreement, so that the choice of parliamentarians is reduced to what it calls a "version" of its agreement on Brexit, or no Brexit (through a referendum).  It should and this increasing probability that we will remain in the EU, after all, will lead the Prime Minister to start dealing with Jeremy Corbyn, to agree on a vision of the future UK trade relationship that could command the majority in the Common Commons ?
An influential minister told me: "My judgment is that Corbyn would never compromise on any agreement because it needs a crisis and general elections, so moving to a softer Brexit loses only more conservative votes [MP] without earning a lot of Labor. "
Seems like no attempt at May
Ministers presume that the Prime Minister would have a last time with EU leaders to persuade them – despite all their protests that this can not happen – to open the Withdrawal Agreement and formalize the temporary status of the backstop, creating a mechanism that would give MPs greater confidence in their power.
But here we return to Catch 22 of the Prime Minister's decision-making process.
The leaders of the EU are not convinced that if they did what they would see as the mother of all weather conditions, effectively burying the obstacle, Theresa May would even have won her vote – because of # 39 absence of any consensus in parliament on what should be the future relationship with the EU.
The correct point of view in European capitals, given by an official of one of them, is that MPs Brexiter and Remainer reject the withdrawal agreement for several reasons: "The backstop is not the only one problem for both these groups. "
Unless May succeeds in persuading EU leaders that she would win the vote in the wake of a fall on the seabed, there will be no humiliation of such a withdrawal.
We are going, as the Prime Minister warned, for unexplored waters. And Theresa May – someone would say – has only herself to blame.