Since will whip in favour of the Letwin amendment, it is now impossible for Boris Johnson to view it as anything but inimical and hostile to his ambition of getting the UK out of the EU with his deal on October 31.
Secondly, as a way to frustrate passage of the Withdrawal Agreement Bill, attaching its own Brexit stipulations to it, and probably pushing an amendment that would make any Brexit approval conditional on the UK holding another referendum.
Johnson tonight has three choices.
He could call the bluff of Tory, ex-Tory and Brexit-y Labour supporters of the Letwin amendment, and promise them the guarantees on workers rights and environmental protection they seek - thus in theory obviating the need for Letwin’s sought delay to Brexit approval.
Or he could tell his own MPs that voting for Letwin is plainly a vote for his deal, as Letwin claims it is, thus claiming a victory via textual interpretation from the jaws of defeat.
Or Johnson could say it is his way, his motion passed unamended tomorrow, or straight back to the short path to a no-deal Brexit.
Letwin thinks he has created conditions for a more sober and orderly Brexit.
But if his motion passes, and the PM interprets that - as I am sure he will - as a hostile act.
Letwin knows (because he is not naive) that days of chaos will ensue, when we can’t know whether Brexit will be delayed, whether it will be cancelled, whether a no-deal Brexit is back on or whether the government will fall.
Nothing much at stake tomorrow then.