Hope of any form of compromise between the Trimble and Donaldson wings of the UUP has dissolved in the run-up to tonight's Ulster Unionist Council debate.
Both the party leader and Mr Jeffrey Donaldson, who is vice- chairman of the UUC, are diametrically opposed on key elements of policy regarding the Joint Declaration. This was drawn up by the two governments at Hillsborough in April and was designed to map the way towards implementation of the Belfast Agreement in return for an end to paramilitarism and the removal of illegal weapons.
The decision on the Joint Declaration to be taken by the UUP's ruling body this evening represents a crunch for both men and their wings of the party. The tactics to be adopted by the loser of the vote could radically alter the face of the party and provoke a realignment in unionist politics.
The de-facto heads of the rival groups within the party have written to the 860 UUC delegates outlining their positions and calling for support. The letters, copies of which have been seen by The Irish Times, illustrate the deep divisions between Mr Donaldson and Mr Trimble.
The language used by both is uncompromising with Mr Donaldson asserting that the leadership has not made a coherent argument in favour of the Joint Declaration and Mr Trimble accusing his opponents of publicly tearing the party apart.
Mr Donaldson views the meeting as a "defining moment for unionism" and is making clear his criticisms of the Trimble leadership and what he sees as the electoral damage it is causing his party.
Unionist insiders close to Mr Trimble, however, predict he will win any crunch vote this evening and defeat the Donaldson push to have the UUP reject outright the terms of the declaration.
Mr Trimble will propose a six-point amendment to Mr Donaldson's motion which demands the rejection of the Joint Declaration. These amendments soften opposition to elements in the document but do not imply acceptance either.
Unionists acknowledge the hopeless split in UUP ranks and accept that a win for one side will only mean a damaging defeat for the other which will probably result in some members, perhaps including Mr Donaldson, quitting the party.
He continues to insist he will "consider his position" in the event of defeat at the UUC, but will not elaborate. In an interview at the weekend, Mr Trimble insisted he wanted to remain at the helm of the UUP to finish the job he had begun.
Exchanges between Mr Donaldson and his party leader have grown in antipathy. The Lagan Valley MP, who walked out of talks on the night the Belfast Agreement was concluded, claims Mr Trimble is behaving foolishly.
"The days of constructive ambiguity are at an end. We cannot fudge this issue of the Joint Declaration. Foolishly believing we can cherry-pick the document flies in the face of reality."
Mr Trimble accuses his main critic of letting republicans off the hook by drawing all attention on party policy and away from calls to end paramilitary activity as demanded by Mr Blair.
Mr Donaldson cited the discovery yesterday of a 1,200-pound bomb in Derry as evidence of the continuing republican paramilitary threat. He has made political capital out of talk of disbandment of the home battalions of the Royal Irish Regiment, suggesting the declaration is soft on the IRA - a sensitive topic for UUC delegates.
He further claims the declaration will bring about a scenario where paramilitary disbandment and disarmament will not be timetabled, where the Irish Government will have "a significant role" in Assembly affairs, and where Northern Ireland will see further British demilitarisation and devolution of justice and policing powers which could go to a Sinn Féin minister in a restored Stormont.
The UUP leader says he shares "many of the concerns about the Joint Declaration" but urges delegates to accept that "we will not persuade by adopting unreasonable demands, or appearing to constantly be looking for an excuse to say reject and run away".
Tonight's UUC meeting is the 11th on issues linked to the Belfast Agreement since 1998.
Mr Trimble has held on to victory by various margins at previous gatherings, but this evening's is certain to inflict a defeat on one side which could well alter the face of the UUP, and by implication, the whole of Northern politics.