Here is the measure of today's events in Parliament: probably the least important question is whether the PM names her own departure date when she sees a rowdy meeting of Tory MPs at 5pm under the umbrella of the 1922 Committee. This is not to trivialise whether or not she confirms she would stand down on May 22nd or shortly afterwards, subject to her Brexit deal being ratified later this week. If she conveys in any way when she's going, and her colleagues have no idea whether or not she will, that's huge.
But every Tory MP knows she is a short-dated Prime Minister. Whatever Theresa May says today, none of her MPs expect the leadership election that would select her successor to be held later than the summer.
More important is whether up to 20 of her junior ministers feel they have to resign if they are whipped to stymie backbench MPs taking control of Monday's parliamentary business (probably needed for MPs to whittle down popular alternative Brexit options to just one). Or if they feel the need to resign due to being whipped to vote against rivals to May's Brexit plan that she hates and they like (to remind you, I yesterday said I thought there could be 10 ministerial resignations in those circumstances).
What the PM probably fears most is that MPs coalesce today around one of the two customs union motions – J and F – put down respectively by Ken Clarke and Gareth Snell. Both are consistent with Labour policy, so you would expect Labour to whip in favour of them. Both are inconsistent with the Tory manifesto, so you would expect the PM to whip against them. Both could be tagged on to the Withdrawal Agreement, to create a compromise that would be accepted by the EU and deliver Brexit – and even probably allow exit on May 22nd. Both would split the Tory Party, because hardline Brexiters hate that they would proscribe the UK from negotiating free trade deals (they are 'good-night-and-good-luck-to-Liam-Fox' motions).
'We're on the glide path to the Customs Union' said one minster – I won't share with you whether said minister views that prospect with delight or horror. By the way, the PM's third meaningful vote on her Brexit deal could yet be tomorrow. That's because of growing optimism in Downing Street, and among the whips, that momentum is now with the PM, following the softening of opposition to it from Jacob Rees-Mogg and Boris Johnson (yesterday I said I expected the vote on Friday, and it may still happen then – if at all).
It really matters though that Rees-Mogg and Johnson have set, as a necessary condition for their u-turns, that the DUP u-turns too and first – and I see absolutely no sign of the DUP capitulating. The PM has not yet banked their votes for her deal. Even if in the end, she secures Rees-Mogg, Johnson and the DUP's 10 MPs, she certainly has not captured the entire Tory rebel crew of the European Research Group. My estimate is that up to 30 Tory ERG Brexiters will vote against an unamended Withdrawal Agreement till they breathe their last breaths. And the chances of the PM wooing sufficient Labour Brexiters to make up the difference is less likely than Jacob Rees-Mogg becoming the next leader of the Labour Party.
I don't see how she wins her meaningful vote this week – unless somehow today's indicative votes terrify enough Tory and Labour Brexiters into thinking all Brexit would be lost if they don't surrender to her. Which completely jars with what I know of their motives and characters.
Robert Peston is ITV’s Political Editor. This article originally appeared on his ITV news blog