They will make history in Northern Ireland next week. That much at least is certain.
Good or bad? Success - sweet with the promise of new beginnings? Or another historic failure - the sour certainty of a return to the past? Few, wisely, would predict. Those who raised themselves this time last year to say there was no possibility of a deal were confounded by the events of Good Friday. And by the first calendar anniversary of that unforgettable day, the Ulster Unionists and Sinn Fein might be sharing in the government of Northern Ireland. Or not.
Even as they profess no knowledge of the means of delivery, the British and Irish governments maintain dogged belief that the new administration will arrive safely, on or about the due date. On all the evidence available, however, it is also objectively right to say it might be still-born. As the mood in Belfast turned distinctly downbeat, a senior British source last night warned against "the Good Friday illusion" - the complacent assumption that, as the rabbit was pulled out of the hat last time, so it would be again.
British and Irish officials are working flat out this weekend on a package of measures around which they desperately hope to frame a solution to the decommissioning issue. Apart from the promise of executive posts, the swift formation of the North-South Ministerial Council and the full-blooded implementation of the Belfast Agreement, the package is likely to focus on key confidence-building measures directed at the nationalist and republican communities.
New emphasis and impetus may be given to the Commissions on Equality and Human Rights. And the long-awaited British paper on the "normalisation" of security arrangements in the North is clearly intended to make a crucial contribution. The First Minister designate, Mr David Trimble, has not yet been made privy to its contents. And there is clear apprehension in unionist circles that it might contain proposals for a Dunblane-style ban on the possession of personal firearms.
Unionists would be expected, almost as a matter of form, to be critical of any British contribution to the "demilitarisation" process. And some sources predict a somewhat ritualised element in any angry response from Mr Trimble. There may be. However, that could prove yet another complacent assumption.
By general consent, the last two weeks have been pretty disastrous for the Royal Ulster Constabulary. There is no doubt that questions about the force, and its failure as an institution to regulate itself, now extend far beyond the republican constituency. Among a sizeable section of the unionist constituency, however, the belief remains that the now rapidly escalating campaign against the RUC is proof that nothing really was settled last Good Friday, and that Sinn Fein and the republican movement intend to continue to radicalise nationalist opinion and destabilise Northern Ireland.
No matter that, to the outside observer's eye, that very option would be denied Sinn Fein, should the party get to take its place in government. No matter that, in the minds of many, elements within his force have themselves contributed to the difficulties now confronting Sir Ronnie Flanagan, and to the further radicalising of nationalist opinion and sentiment.
This unionist perception runs deep, and it will hardly have been diminished by Mr Adams's assertion in this newspaper last week: "Before the Good Friday document, the six-county state was an undemocratic, illegitimate and failed political entity and after it, it remains so."
The UUP leader might calmly retort: "He would say that, wouldn't he?" He plainly considers it so much bunk, and believes Mr Adams knows it as such. However, Mr Trimble is frequently frustrated by, yet must still contend with, the readiness of many unionists to believe the republican account. Past experience inclines them to suspect that the Belfast Agreement is indeed, as Mr Adams says, "but a part" of a wider and "ongoing" process.
It might also be said that Mr Trimble and his team have been altogether abysmal in selling their alternative view, that the agreement settled the constitutional issue and removed the basis for the IRA "war" by tying all parties to the principle of consent. Throw into the stew the republican/ nationalist belief, and corresponding unionist fear, that the ground has significantly shifted in the debate over the future of policing, and we have a reminder of the dangerous path Mr Trimble walks.
Sinn Fein routinely dismisses talk of Mr Trimble's internal party difficulties. But if it has any serious doubt, it should examine the results of last Saturday's elections for top posts in the ruling Ulster Unionist Council. While the delegates were able to support candidates for four posts in the honorary secretary and vice-president sections, party sources confirm that hundreds of ballot papers reflected a clear pattern of pro- and anti-agreement voting.
The results left the leading Trimbleista, Sir Reg Empey, with 430 votes in the VP ballot, to 398 for Mr Jeffrey Donaldson, who headed the anti-agreement slate in a clean sweep of all four honorary secretary posts. Moreover, the Rev Martin Smyth topped them all, reclaiming his post as vice-president alongside Empey, Ken Maginnis and Jim Nicholson, with 501 votes.
The spin on this is that Mr Smyth, as a respected party man, claimed support from both sides. But even allowing for that, and the personality factors at work, the evidence suggests an Ulster Unionist Council more or less split down the middle, and, thus, a significant movement of internal party opinion against the agreement since last year.
This will weigh heavily with the UUP leader as he joins Mr Blair, Mr Ahern, Mr Adams and the rest for next week's make-or-break talks at Stormont. For the likelihood is that the Ulster Unionist Council could be meeting again, in emergency session, in the very near future. Anti-agreement unionists would plainly have no difficulty gathering the requisite 60 signatures to trigger such an event. And a leading dissident source last night confirmed this would happen within days, should Mr Trimble enter the executive with Sinn Fein without actual decommissioning, or, accept a gesture which failed his own declared requirement that it should be "credible" and mark "the beginning of a process".
Citing past evidence, some implacable opponents predict Trimble will crumble. However, even stern party critics profess themselves content he will not. And within the rival unionist parties there is a grudging (though not unanimous) suggestion that he will hold the line, if only because, as they see it, he has to.
Among these disparate forces the still-more contented belief is that the executive will not be formed, because the IRA will not deliver on decommissioning. British and Irish sources admit they have no evidence to suggest otherwise. The loyalist parties, the PUP at any rate, do not believe it to be in Sinn Fein's gift at this point. And those with an eye for these things find it almost unimaginable that an act of IRA decommissioning could provide the precursor to the annual pilgrimage to republican gravesides, and the Easter Rising celebrations. Presumably such calculations were swirling in John Taylor's mind last Tuesday, when he reportedly advised the UUP Assembly members to prepare themselves for six months' unpaid holiday.
There is too, of course, a darker analysis, which suggests the republican movement might not be totally unhappy to see the agreement fail at this point. Something of that was reflected in Thursday's threat that the UVF and Red Hand Commando would "retreat from all theories of process - peace or political" in the event of an "imposed" settlement. The scenario to which they appear to be looking is one in which the republicans lose the bits of the Belfast Agreement they don't much like, and cheerfully observe unionism further fragment in a welter of recrimination, while a summer of discontent (fuelled by the marching season, the European elections, and hopes and fears for the Patten Commission) drive nationalist Ireland toward a renewed consensus on the need for a solution, with or without unionist support.
It seems plausible enough, though it must be said it does not accord with the British or Irish assessment of the Sinn Fein leadership's intention or desire. Mr Ahern and Mr Blair will be relying on Mr Adams's understanding that, whatever the apparent attractions of such a course, there would be no guarantee that the republican movement could control the consequent events, still less that those events would permit any easy or automatic return to politics further down the line.