It is possible that Boris Johnson’s government will fall today, or in effect fall.
There are now said to be at least 21 Conservative MPs who will stand up to him on Europe.
These are people who feel more strongly about the EU than they do about the Tory party.
Therefore this moment has been a long time coming. The only thing that was, and remains, uncertain is the number and the timing of the split.
Certainly, if that number of Conservatives vote against the party, or leave it, or are banished from it, Boris Johnson will be unable to continue as prime minister.
It is greater in number than the Labour MPs who have quit Jeremy Corbyn’s party, or who are so pro Brexit they will back the prime minister.
Having said that, it is far from clear how the government will actually fall. It might be that MPs pass some attempt to force the PM to extend our departure from the EU, that he refuses to do that, calls a general election, but fails to muster the numbers needed for such a poll under the Fixed Term Parliaments Act.
Therefore, in multiple ways we are in unprecedented constitutional territory. But it is hard now to see this government holding things together beyond October 31.
There are now major risks for unionism.
If Mr Johnson gets an overall majority, he might push through the disastrous backstop that he voted for in March.
If a Labour SNP coalition can be formed, it might do the same and also call a border poll.
One thing unionists must now do, ahead of the visit by Michel Barnier next week, is make clear again and again the scale of opposition to the backstop, which does major constitutional damage to NI’s place in the Union.
Supporters of the backstop have been much better organised and have allowed Mr Barnier to claim to be supporting peace here.