Just been reminiscing with someone about the 2015/6 days of local party meetings, and the image that kept coming to mind is of a wave endlessly crashing against a brick wall.
Some further thoughts: Early meetings were packed and then that dropped off very quickly - my sense was that the 'old guard', even if they were pro-Corbyn, didn't really know what to do with the new intake.
so they carried on discussing potholes and organising factionally in an opaque way. As someone who has been going to local meetings for 20 years, there was a real difference in 2015/6 but also an obvious unease and desire to return to the familiar sparsely-attended days of yore.
One solution to this would obviously have been to unseat and replace these people with more enthusiastic militants, but the consciousness and knowledge base for how to do that wasn't there, so even in branches where Momentum were strong, the right was able to retain control.
At elections we did have a really good ground game, but elections are where the party machinery knows how to use a mass membership, so that was no real surprise (other than there being far greater numbers to be deployed than in previous years).
I went to an absolutely massive meeting of "Haringey Momentum" in 2015 but in the next few months it just seemed to dry up entirely. The organisation became a mailing-list and an electoral machine, rather than aiming at any kind of social transformation.
Another unhelpful thing was the sects trying to muscle in on Momentum immediately, which I think rightly made the old guard suspicious of newcomers.
On the plus side, the Corbyn years did feel like being part of a movement, a determined and united collective - I hadn't felt like that before as a party member! It's just that the movement didn't actually move anywhere.
I guess The World Transformed is the biggest initiative that came out of Corbynism, and I do think that's useful and should be sustained and expanded if it can be.