The biggest question currently gripping most of the Labour Party and the trade union movement is how far Unite will move next week at its biennial policy conference to support a referendum on the terms for the UK leaving the EU, as and when they are known.
Because it is widely believed that if Unite, as the party's paymasters and supplier of important officials, were to back another plebiscite, so too would Jeremy Corbyn.
It is quite clear, from the preliminary motions submitted by Unite branches, that many Unite members would like the union to come out in favour of another vote.
Their numbers won't have been diminished by the growing volubility of big employers about the negative impact on jobs and investment of significant new frictions and costs being introduced into UK trade with the EU single market.
I am told that Len McCluskey does not want to commit the union to another referendum - or at least not yet.
I understand the powerful Unite general secretary hopes to broker a compromise which would keep open the option of Unite coming down in favour of the referendum in the autumn, and doing so on the basis of leadership fiat rather than a further consultation with members.
This would be more-or-less consistent with Labour's official line, which is that it will judge whether it would support a Brexit deal or no-deal according to its six so-called Brexit test (which are not really tests in the common sense meaning of the word - since these ones are definitionally impossible to pass).
Normally McCluskey gets what he wants. But he is under pressure to leapfrog Labour and commit now to a vote.
So paradoxically he may well be desperate for Labour moderates led by Chuka Umunna to weigh in and pressurise his members to lobby for a referendum - because he is confident that Umunna and co are so mistrusted by trade unionists, and by the Labour leadership, that anything they do to drive a wedge between him and his members will have precisely the opposite consequence.