Whether HoC is able to legislate an extension or not, an election will come. And Johnson will be able to blame any extension ("Corbyn surrender") on Parliament.
1/
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Or we get a people vs parliament election.
And before that election, the Tory party can morph into the Brexit Party, by deselecting Remainers & soft-Leavers.
3/
So, this is the Cummings/ Johnson plan in action.
Again, I may be missing something, but IMO it is much too early to declare that "Cummings overplayed" or "Boris has been defeated"
/end