A serious question mark has been raised over Sinn Fein's continued participation in the Stormont Assembly should the Mitchell review fail to secure agreement this week on the formation of the power-sharing executive.
And with few participants prepared to predict a successful outcome for the review, some hopes are being placed in a suggestion that Gen. John de Chastelain, the head of the International Decommissioning Commission, might be called upon to effectively by-pass the political parties and make a direct overture to loyalist and republican paramilitaries.
This emerged last night after another day of intensive talks in London apparently produced no significant movement on the key issues at the heart of the political impasse threatening the Belfast Agreement.
Usually reliable sources said the doubts about Sinn Fein's willingness to remain at Stormont surfaced yesterday as Sinn Fein repeated it could not meet the UUP's demands for IRA decommissioning as the price of the party's entry into government.
Some talks participants saw the threat of a fresh political crisis as an attempt to put pressure on the SDLP; others as predictable "hardball" by Sinn Fein ahead of crunch talks scheduled to resume in Belfast on Friday and Saturday. Authoritative sources indicated last night that Senator George Mitchell is determined to bring the review to a conclusion by the weekend.
However, despite general insistence that the "atmospherics" and the "engagement" between the parties is better than before, the stakes were clearly being raised on all sides as senior Ulster Unionist negotiators insisted: "Unless there is actual product [weapons] there is no deal."
Sinn Fein sources earlier confirmed they had told the Ulster Unionists they could not give Mr David Trimble the "commitment" he seeks binding the republican movement to an "obligation" to decommission with an indicative timetable for actual delivery. The party is understood to be ready to repeat language which first appeared in July, expressing confidence that its influence could be successfully deployed to secure eventual decommissioning.
However, it is unclear whether there is agreement that the IRA should appoint an interlocutor to deal with the international commission. And there is as yet no evidence of any willingness to enter any private understanding as to how quickly any decommissioning would follow the creation of the executive, of the kind which apparently prompted the British Prime Minister, Mr Blair, to proclaim a "seismic shift" in republican attitudes in July.
Unionist sources insist Mr Trimble's position is equally clear and unchanging, namely that the two sides will have to "jump together", and that the "sequencing" which would allow the prior creation of the executive will only be considered in the context of a firm commitment to decommissioning in accordance with the modalities and timetables indicated by the commission.
Supporting evidence that Mr Trimble probably does not intend to shift position is perhaps to be found in the fact that two issues which attended the July talks are apparently absent this time. First, the UUP leader is understood to have rejected the suggestion that he should form the executive while placing a post-dated letter of resignation with the Assembly Presiding Officer, to take effect should decommissioning fail to start by a designated date.
Second, it appears that in this round of negotiations the Ulster Unionists have not so far raised the vexed question of the "sanction" to be applied against Sinn Fein alone, should decommissioning not occur. Close observers are agreed the implication clearly is that Mr Trimble simply does not foresee that situation arising.
Despite earlier suggestions that Senator Mitchell might report limited progress this week, and promise to return at a later stage, most parties now seem to accept this is unlikely. Significantly, perhaps, official sources are making it clear that the two governments are not proceeding either on the assumption that the review will necessarily succeed, or that failure would mark the end of the road for the agreement.