Mr David Trimble, the First Minister, suspects the North's political process will be adjourned in crisis by the end of this week.
This became clear last night as the Taoiseach, Mr Ahern, and the British Prime Minister, Mr Blair, prepared to travel to Belfast in a final attempt to save the Belfast Agreement.
The Ulster Unionist leader apparently still believes the Provisional IRA will ultimately concede on the decommissioning issue, but thinks the republican movement is undecided on the issues of timing and content.
Bitterly critical of Dr Mo Mowlam's decision to drop the March 18th target date for devolution, he has never been convinced that a republican concession was the more probable in the week preceding the Easter Commemorations. And, barring a breakthrough this week, he and his strategists think Dr Mowlam's commitment to trigger the d'Hondt mechanism for the creation of the executive on Wednesday or Thursday more likely to trigger a "soft" or "crash" landing for the entire process.
The potential collision is spelt out in Dr Mowlam's commitment to discharge her obligation and push for the creation of the executive - and Mr Trimble's corresponding commitment to seek Sinn Fein's exclusion from office if a credible start has not been made to decommissioning.
All of this will, of course, be academic if Mr Ahern and Mr Blair can forge a breakthrough in the next 48 hours or so.
However, if Dr Mowlam pushes ahead with d'Hondt in the absence of a prior decommissioning deal, the divided unionist forces in the Assembly look set to coalesce behind a common motion seeking to block Sinn Fein's entry into government.
The arrangements for this were reportedly concluded at meetings last week. The DUP has tabled its motion, bearing the signatures of 29 anti-Agreement unionist Assembly Members (including Ulster Unionist Mr Peter Weir). Mr Trimble has 27 signatories in his back pocket (the two Progressive Unionist members are expected to abstain) on a motion couched in similar terms.
The debate on such a motion (the two sides, in such an event anticipate easy agreement on a common draft) would take precedence over the order to implement d'Hondt. Mr Peter Robinson, of the DUP, calculates that any move by Dr Mowlam to commence ministerial appointments on Wednesday morning would see the Assembly debate in full session that afternoon.
Hence some growing speculation last night that the wee small hours of Tuesday night/Wednesday morning might very well provide the effective deadline for a decision on the issue. Hence, also, the growing belief that, if they conclude that agreement on decommissioning is not on offer, Mr Blair and Mr Ahern might move to prevent a showdown on d'Hondt and the unionist motion to exclude Sinn Fein.
The rationale behind such speculation is that Mr Blair and Mr Ahern would want to avoid a situation in which Mr Trimble and his colleagues cast their votes for Sinn Fein's exclusion. This would open Mr Trimble to instant ridicule from his temporary allies - while, more crucially, polluting the atmosphere in what Sinn Fein would consider an acid test of his bona fides on the agreement itself.
Faced with such a scenario, the two prime ministers would have a number of contingency options.
In the most benign set of circumstances - if it appeared that the symbolism of Easter was an obstacle to an agreement that might otherwise be available on decommissioning - the two leaders could simply adjourn the discussions and further extend the deadline.
If, in fact, they had concluded no agreement was forthcoming, they could forestall the Assembly showdown with Dr Mowlam - either by opting to suspend the Assembly itself or, alternatively, by announcing a review of the Belfast Agreement.
The former would appear highly unlikely, although there have been hints that the Secretary of State in such circumstances might seek to hit the pockets of Assembly members. The latter - which could presumably be open-ended, or time-specific - would provide the "soft landing" Mr Trimble first mooted back in January. It would also have the merit of keeping hope alive.
However, it seems clear the two governments would be brought to this option only very reluctantly. The argument against is well-rehearsed: that the advent of the European elections, the marching season and a summer of mounting agitation about the Patten Commission could dramatically change the Northern political landscape for the worse.
So it can be taken as read that when Mr Ahern and Mr Blair open their series of meetings tonight (in the first instance with the four major parties) they will be pressing for a deal which allows all the institutions prescribed by the agreement to be brought into being without further delay.
Neither government has yet been prepared to concede that Sinn Fein cannot deliver actual IRA "product". The Taoiseach apparently accepts that Mr Trimble will not be able to move without it, and Mr Blair recently enraged the Sinn Fein leadership by suggesting it could deliver if it wished to do so. The belief appears strong in Dublin, moreover, that a gesture by the IRA might be enough to have the whole issue then deposited at the door of Gen de Chastelain, while getting Mr Trimble off the hook of "benchmarks" and "process" guaranteeing total disarmament by May 2000.
A variation of this theme is that, if the IRA remains insistent it will not decommission at all as the price of Sinn Fein's entry into the executive, Mr Trimble might accept a post-dated promise (presumably deemed watertight by Gen de Chastelain) to do so swiftly after its creation, whether in shadow or substantive form.
The problems with this option are obvious. Firstly, Mr Trimble could hardly keep it a secret. Secondly, as one close observer put it last night, the delivery date would have to be early indeed - early enough to pre-empt dissident unionists convening an emergency meeting of the Ulster Unionist Council to denounce a "sell-out". Thirdly, and in consequence, that the republican movement's "victory" on the theological point of "no preconditions" would be covered by a very thin fig-leaf indeed.
In an atmosphere of increasing speculation and anxiety last night, still more imaginative solutions were being canvassed. Of these, the most intriguing, and one apparently enjoying some American support, is that the paramilitaries might vouchsafe control of their weapons dumps to the International Commission. Based on a legal concept governing trusts, the idea appears to be that a nominated representative of the respective paramilitary organisation and the Commission would have access to centralised dumps, which would be open to periodic inspection, while technically remaining in the "ownership" of the paramilitaries and covered by the immunity provisions already in place.
Usually reliable sources say, however, that even if the paramilitaries were to contemplate such a move, such a set of arrangements would be unacceptable to two democratic governments. (Nobody, by the way, appeared to have answers to two fairly obvious questions. Why would the paramilitaries not see this as a "surrender" of their weapons? And, even if they were prepared to act on trust, what would happen if they ever asked for their weapons back?)
Both governments might well be prepared to press Mr Trimble to accept the solution again canvassed yesterday by Mr Seamus Mallon in the Sunday Independent - the dropping of the prior decommissioning demand, in return for a definitive agreement spelling out "that it (decommissioning) will be done, how it will be processed, and that it will be completed within the time specified in the Agreement."
The Ulster Unionist security spokesman, Mr Ken Maginnis, appeared to open the door to this possibility some weeks ago in an interview with the London Times, when he said it was "the certainty of achievement" rather than the modalities which mattered most to his party. But that brought an apparent rebuke from Mr Trimble, who seems to have vested everything on up-front delivery.
This would suggest that, for all the variety of imaginative schemes on offer and still to be dreamt up, the heat this week will be for a republican gesture of good faith.
Mr Trimble says any such gesture must be "credible" and that he will know what "credible" is when he sees it. But, even if he came to the conclusion that delivery was in his gift, would that be good enough for Mr Adams?
The Sinn Fein leader has spoken of his willingness to again stretch the republican constituency, but equally of his determination that he and Mr Trimble must be in the same loop if and when they jump.
Whatever Mr Adams has in mind, he is signalling that he won't be delivering anything unless first satisfied that it will be enough, and that Mr Trimble, without further prevarication, will keep his side of the bargain.
Knowledge of the downside for Mr Trimble and for unionism - should he promise and subsequently fail to deliver - seems the best hope still that Sinn Fein will put him to the test.