The centre-left and the radical left are going to have to find some way of either coexisting or cooperating. I won't rehash the terrible history of sectarianism on the left, but will just mention that the split between the German Social Democrats and the Communist Party was a clear enabling factor in the rise of Nazism.
Surveying the left across the West we find different manifestations of the same problem: a split between centrist social democrats and more radical leftists. Spain just had its second election in six months, one where the left in the form of Podemos was expected to overtake the centre-left PSOE. But unlike Pasok in Greece, Spanish social democracy is refusing to die. In the USA Bernie Sanders could not defeat Hillary Clinton, despite the broad enthusiasm, energy and grassroots funding he managed to raise.
And then there's Britain, where these two tendencies are embodied in one dysfunctional party. The broad centre-left of the Parliamentary Labour Party has struck out against the radical leadership of Jeremy Corbyn.
Both sides need to accept that they lack the popular backing and material resources to win alone. Radical support is concentrated in big cities and is often young, with some links to older workers with memories of long-dead industrial struggles. The centrists tend towards the older, wealthier working class and progressive, well established middle classes. What's missing is the classical organised working class, the disappearance of which is at the root of the split between the two sides.
While neither side can win alone, they cannot function as a single electoral party either. But if they fail to find some formula for coexistence we know the likely outcome: victory for the radical right.
So, here is a simple proposal for uniting the British left: first, radicals should support Jeremy Corbyn and encourage an open, democratic leadership election. We should do so while talking to the broad British public, promising to have our ship in order come a general election.
Secondly, we should accept it if Corbyn loses. I am inclined to resign my Labour membership in that case, but I will pledge to work in a non-sectarian way with people who remain. At the grassroots we aren't really all that intolerant. I'm sure we can continue to work across parties and outside them.
Thirdly, in the event of a Corbyn victory we should approach the centrists with a clear electoral offer: if the radical leadership loses seats at a general election, Corbyn will stand aside and, if we can, we'll field another candidate. We should also invite their input on crafting a Brexit negotiation package that will include an open immigration policy.
Fourthly, we will expand Labour involvement in anti-racism campaigns. We should devote increased funds to social inclusion and education in communities. Labour should be at the forefront of these campaigns.
And finally, if Corbyn is kept off the leadership ballot on a legal technicality, doesn't make the necessary number of MPs, or loses the election we accept it but begin work on forming a new party, which will take Corbynism out of Labour. This formation would seek to build campaigning alliances with other progressive parties and movements.
To be clear: none of the above proposals is intended as succour for those who wish to "heal the wounds in the Labour family." Instead each would allow the laying of the foundations for an eventual split. Only by formalising the de facto split which is already tearing the party apart can the two sides conceive of each other as equals - distinct sides with competing, equivalent claims that can be legitimately negotiated between. The split would in fact aid cooperation between the two sides.
The centrists could swat down each of these moves - this is after all about power. But there is little we on the left can do to alter the other side's sectarianism. We can reach out to them in full knowledge of the gravity of the situation. We may not be able to persuade them or even to function productively alongside them. But we should still try. If we are forced into fighting, we will have to do so.
The status quo is not on offer. The other side is too powerful to beat outright: they have almost all Parliamentary positions and most of the media. We have the grassroots and the (historically very weak) trade unions. We need to institutionalise our antagonisms, making explicit the two sides' goals, and finding a way to cooperate.
Allowing ourselves - the radical left - to become fully subordinated to the centrists again will only cost us in the long run. Labour will remain undemocratic and neoliberal whilst its vote shrivels further. We should seek to make the divide between the centre and the left explicit and to make it as collaborative as possible. If we can't win over Labour MPs, we should open up campaigning ground which is autonomous from the Labour Party but still willing to work with it. These ideas my be unrealistic. But the alternative is disaster guaranteed.