Truthfully I don't really understand why the prime minister is holding a vote on Friday to approve the Withdrawal Agreement she negotiated with the EU - other than the symbolism of showing that on the day she originally set as Brexit day, 29 March 2019, she is still working hard to extricate the UK from the EU.
Because I don't see how she wins it.
It's almost irrelevant that Friday's vote won't be a "meaningful vote", under the terms of the EU Withdrawal Agreement act.
It is to all intents and purposes a meaningful vote: if the motion laid tonight is passed on Friday, MPs WOULD be approving Brexit, under the terms laid down by the EU 27's leaders a week ago.
And if the motion were passed, the UK would be leaving the EU on May 22 (and as a side effect, elections would be triggered for a new leader of the Tory Party and new prime minister, as a result of what the PM promised her party yesterday).
If rejected, we're out on April 12 without a deal, unless another way can be found to persuade the EU to delay Brexit.
For the PM, the idea that on Friday the UK will know it is leaving the EU and that she will know she is escaping Downing Street looks like wishful thinking on an epic scale.
Her motion looks defeated before even being discussed.
Northern Ireland's 10 DUP MPs have told me they will vote against it, which means 30 or 40 Tory ERG Brexiters will vote against it.
And given that voting for the Withdrawal Agreement on its own, without any framework for the future relationship with the EU, means MPs are being asked to vote on the blindest Brexit, all but a tiny number of Labour MPs will oppose it.
I asked a number of ministers why the PM was setting herself up for further humiliation in this way.
There was much scratching of heads: "None of us know" said one, "I'm quite anxious".
For what it's worth, and I pass this on not because I believe it true but because the sources are credible, there is a view in Whitehall and among some ministers that it's all about setting up a choice for the UK between a long Brexit delay and a no-deal Brexit on April 12.
And having given signals that she hates both no-deal and long delay, the PM is preparing to jump for no deal, they say.
They may be wrong, but if no-deal Brexit is really Theresa May's Plan B, the House of Commons does not - as yet - have a device to stop her.