The bulk of the Left of the Labour Party, having thoroughly swallowed the mendacious soft-focus "I'm really a Corbynite" leadership pitch of Kier Starmer, rapidly became disillusioned (and in some cases, defenestrated) when he started purging the Peoples Party in a singularly calculating manner.
And we know whose are the calculations: it's Mandelson, the preeminent British political strategist of the age.
I feel we may now summarise his 2019 thinking, and estimate his chances of success.
1. Corbyn has done a Thatcher**, potentially sterilising the Labour vote for years to come
2. The only chance of reversing that lies in someone who looks the part (besuited, established), grabs all the levers of power within the party AND ...
3. ... methodically, gratuitously, ruthlessly and flamboyantly takes every opportunity to do Corbyn and his acolytes down (in ways that Hague, IDS and Howard could never do to Thatcher). You don't want an excrescence of people who remind the electorate of Corbyn and, crucially, you don't need them; neither for their pitiful subscriptions NOR as election-time infantry - because elections are lost by sitting governments, and won by clever media strategies funded by big donations, not knocking on doors
4. Johnson is always going to self-destruct: possibly sooner rather than later: the key is to be in position for when it happens