Theresa May made a last minute plea to MPs to give her Brexit plan a second look - but despite putting on a brave face even she knows that victory is next to impossible.
The only question today is the scale of defeat that the Prime Minister will suffer.
It's a sign of her political fortunes that Government insiders were last night saying that a loss of under 100 MPs would really be a win. Her critics were talking of a defeat by up to twice that number.
A Government has lost by more than 200 votes only three times in the last century. If that happens today, it would be the height of humiliation for the already embattled PM.
A total of 117 Tory MPs opposed her in the no confidence vote last month. The whips will be hoping to apply enough pressure in the countdown to tonight's vote to win some of them back. Even if she suffers a loss of historic proportions, she cannot be challenged for the Conservative leadership for another year.
Yet there was speculation last night that the men in grey suits could still possibly come calling to tell her that whatever the official legal position, she could not in reality continue with any authority in the face of such a defeat.
Labour leader Jeremy Corbyn may table a motion of no confidence after Mrs May's predicted loss tonight but, without the DUP's support, it's purely tokenistic and a general election remains highly unlikely in the short term.
With the Withdrawal Agreement defeated, there is no reason whatsoever for the DUP to vote to bring down the Government.
The one consolation for the Prime Minister is that a YouGov poll shows support for the Conservatives is holding up extremely well despite the chaos in the Commons. On 41%, the Tories are a comfortable six points ahead of Labour which has slipped to its lowest rating.
But unfortunately for Mrs May, opinion polls have absolutely no effect on parliamentary arithmetic.
If she is to get the Withdrawal Agreement through the Commons, then the support of the DUP is essential.
Publishing a letter from Jean-Claude Juncker and Donald Tusk was never going to swing it.
Demanding changes to the legal text isn't a negotiating position for Arlene Foster's party - it's the top, middle and bottom line. Perhaps today's predicted defeat is part of the Prime Minister's plan. She knows that realistically compromise won't be forthcoming from the EU until she has exhausted all options for the Withdrawal Agreement as it stands.
Despite the EU's vehemence that the backstop won't be binned under any circumstances, the DUP insist that it is not a pie-in-the-sky demand.
But if Brussels doesn't budge and the choice ends up accepting the backstop or no Brexit, don't be expecting any wobbles and a change of heart from the DUP.
However staunch the opposition to remaining in the EU within Mrs Foster's party, it is trumped every time by the party's determination that nothing puts the Union in jeopardy. And, rightly or wrongly, the DUP believes the Withdrawal Agreement presents a massive threat.