The sacking of John McCallister as deputy leader of the Ulster Unionist Party could yet split the party and lead to the emergence of a new organisation.
Mr McCallister warned in a speech that "reasonable observers are concluding that the UUP is sleep-walking into 'unionist unity'. The recent, almost daily, diet of shared initiatives with the DUP, shared commemorations, shared Press releases, shared events, shared statements, has built up the unfortunate impression that the 'unionist unity' train has left the station. In the driver's cab a certain P Robinson is smiling broadly."
Why did Mike Nesbitt consider that a hanging offence? He plans a mini-reshuffle soon. Would that not have been time enough to abolish the post of deputy leader?
The haste with which he moved, summoning Mr McCallister to a 9am meeting, before leaving for England, suggests that the comments did, indeed, endanger relations with the DUP.
Last Friday, Peter Robinson and Mike Nesbitt both spoke on the subject at an Ulster Covenant dinner. Mr Robinson conceded that this generation might not achieve a single party, but added "there is huge value in unionists working together". He proposed a Council of the Union to entwine all pro-Union elements.
Mr Nesbitt said: "When a united front is required in the best interests of Northern Ireland, the Ulster Unionist party will not be found wanting; but I also want the electorate to have a choice." Ruling out the creation of a single party.
This is a possible basis for agreement. Mr Nesbitt's swift, decisive, high-profile action signalled that he did not want to have his hands tied, or his relationship with Mr Robinson publicly criticised from within the party.
Danny Kennedy, the UUP minister, attends DUP ministerial meetings and Mr Nesbitt regularly meets Mr Robinson.
The Mid-Ulster by-election, which will be triggered if Martin McGuinness fulfils his pledge of resigning the seat, must be on the agenda.
The figures suggest that a single unionist candidate might take the seat. Could that be what Mr Nesbitt meant by a "united front ... in the interests of Northern Ireland"? He won't say.
After Mr McCallister's sacking, Mr Nesbitt quoted the Belfast Telegraph survey at last month's UUP conference which showed 82% of delegates want him to lead the party into the next election.
It also showed that everyone questioned supported his disciplining of Ken Maginnis, which led to the traditionally-minded peer leaving the party. The party likes discipline and Mr Nesbitt may have felt the need to dole some out to a liberal to demonstrate an even-handed approach. Lord Maginnis got no support, but this may be different. One insider described Mr McCallister's treatment as "a tipping-point"; a signal that the more liberal wing may soon need a new home.
Rumours of defections to the Tories have receded; the latest talk is of a new unionist grouping emerging. It might be small, but it could be the beginning of the end of the Ulster Unionist Party.
To avoid it, Mr Nesbitt now needs a plan to satisfy not just Mr McCallister, but also Basil McCrea, Michael McGimpsey and a few others about his future intentions.