In Brexit talks which always seem on the brink of disaster, it's tempting to see as a decisive triumph for the prime minister the decision of her divided cabinet to give her a mandate for the intractable last phase of negotiations.
This would be a naive mistake.
Because although it matters that ministers gave her more latitude to negotiate the so-called backstop - an arrangement to keep open the border between Northern Ireland and the Republic - it would be mad to assume that the other side, Brussels and the EU27, will swallow whatever she serves up.
In fact my strong view, based on soundings made with relevant people on the other side of the Channel, is that issues of very significant principles remain to be resolved - and actually for the UK as much as for the EU.
I am afraid this is dense, complicated stuff. But it matters. So please bear with me.
Let's start with today's reworking by the EU's negotiator Michel Barnier of the cynosure of Mayisms - his statement that "backstop means backstop".
This was not flippant.
It was to make the significant point that there will not be a Withdrawal Agreement, or an orderly negotiated Brexit, unless it contains a guarantee that in all conceivable and notional circumstances the border between NI and the ROI will be kept open.
So this means that even if the EU agrees to May's request that the "primary" backstop should be a UK-wide customs union, and that there would be a process with dual UK and EU controls to terminate the backstop, by definition this could not be the only backstop.
The reason is simple.
The whole justification for a backstop at all is that there is considerable doubt what kind of future relationship and technological innovations could provide an alternative route to keep the border open.
If there weren't this doubt, there would be no need for a backstop, because the new institutional arrangements could be specified now and implementation could start.
So here is the dilemma on whose horns Theresa May may well be skewered.
Any mechanism written into the Withdrawal Agreement that provides certainty to the UK that it could get out of the customs union backstop at some future point is not the "all weather" one that Barnier insisted on again in a tweet tonight.
Which is why he and the rest of the EU, and especially the Republic of Ireland, have not yet abandoned their view that there must be a backstop to the backstop.
And the backstop to the backstop would inevitably apply to Northern Ireland only. So it would be unacceptable both to the PM and the entire cabinet.
In other words, the PM has not yet found a device to eliminate any risk of that which she abhors, namely a new border through the Irish Sea between Northern Ireland and the Republic of Ireland.
That said, if the PM could specify at this juncture a deal that the EU could accept as the long-term relationship between it and us, then the backstop to the backstop would become a disintegrating gossamer, a mere nothing.
But she cannot do that - partly because her first attempt, the Chequers plan with its Facilitated Customs Arrangement, has been rejected by the EU, and partly because the EU is insisting that the future relationship cannot in any legal sense be negotiated till after 29 March next year.
But all hope is not lost.
There is a caveat - which May's Brexiters will find less palatable than a plate of steaming sick.
If May and her cabinet were prepared to say that the UK's ultimate destination, its long term relationship, looked a lot like her preferred backstop, then the backstop would look like a stable and sturdy bridge to a visible and sustainable future - and again the hated backstop to the backstop would become almost otiose.
But she can't say that because that would be to accept two conditions of such horror to her Brexiters that they would probably rather cease being Tories than accept them.
Those conditions would be:
1) The UK would never have the right to negotiate free trade deals with third countries.
2) Brussels would forever set UK rules for consumer, environmental competition and labour standards, to maintain a level playing field between UK and EU marketplaces.
It would be a Brexit that not only doesn't take back control but actually cedes control.
Or to put it another way, her cabinet has not yet been asked to face up to the properly difficult choices that need to be made to reconcile Brexit with keeping open the Irish border.
May told her ministers to keep their diaries flexible enough to accommodate an emergency cabinet meeting later this week or early next to settle a deal once and for all.
I suspect this is when the Cabinet's Brexiter members would finally have to choose between swanky job and chauffeured car on the one hand and their commitment to what they would see as a true Brexit.
Or to frame it in a more altruistic way, they will have to choose between a negotiated Brexit that many of them would see as more notional than substantial and a real or no-deal Brexit, whose hallmarks would be that it is both unilateral and potentially chaotic.