Fourteen years ago to the day Ulster sat, in Mr Peter Robinson's memorable phrase, "on the window ledge of the Union". For the bitter sense of betrayal which swept the unionist heartlands following the signing of the Anglo-Irish Agreement called the very survival of the Union, and allegiance to it, into question.

The irony will not have been lost on the deputy leader of the Democratic Unionist Party yesterday, as he watched another great drama slowly unfold on the Stormont stage.

From Senator George Mitchell - his words as ever carefully crafted, deliberately muted - there were no exaggerated claims of epic events in our time. By virtue of his presence (and the reasons for it) Mr Tony Blair was not there to pronounce that "the hand of history" is upon us. Yet it was, and is.

For after 17 long months of doubt and distrust, Mr David Trimble moved yesterday to secure the agreement which he believes restores the Union to an equitable basis, and which, moreover, obliges Irish republicans to accept the Union's reality for as long as that is the wish of a majority of the people of Northern Ireland.

And despite the conscious lack of histrionics, yesterday's opening gambits by Senator Mitchell and Gen John de Chastelain marked the opening of the sequence intended to see Mr Trimble embrace Sinn Fein in the government of Northern Ireland before the month is out.

Sure, Mr Trimble gave the impression there was everything still to play for - telling people to wait and see what the package is, or if, indeed, there is a package at all. "It ain't over till it's over," the UUP leader insisted, cautioning his audience not to get overly excited about the day's developments.

His chief negotiator, Sir Reg Empey, attempted to sustain the same air of mystery and suspense: telling us what he now needed to hear from Sinn Fein, as if he didn't already know the contents of their eagerly-awaited statement down to the last full stop.

But the dance is on - the sequencing arrangements painstakingly devised during a 10-week negotiation to be played-out between now and Thursday. There is no more hard bargaining to be done. There are no last-minute concessions to be squeezed. For all protestation to the contrary, each side knows what the other is to say. And when, come Thursday, Mr Trimble has heard the IRA endorse Sinn Fein's position, he will seek the agreement of his party officers to put the whole package to the ruling Ulster Unionist Council on Saturday week, as first forecast in The Irish Times.

A lot can happen between now and then. Key UUP players are reserving definitive judgment until they have read all the texts. But at the time of writing, the predictions from leading dissidents are that it will be "very dirty and very vicious" with the outcome too close to call.

ON the face of it, Mr Trimble's position has improved somewhat since last Thursday, when Mr John Taylor's declared opposition persuaded him that he could not appeal to the Ulster Unionist Council without causing a seismic split in his party. British sources have been claiming success on Mr Peter Mandelson's behalf in changing the minds of two of the seven UUP Assembly members who originally declared their opposition.

A number of others have confirmed to The Irish Times their willingness to enable Mr Trimble, as one put it, "to try to manage this through the party". But they made it clear this was without commitment to support Mr Trimble when the issue is put to the vote - or to accept a positive decision by the council unless it is sufficiently convincing and commanding.

"Obviously if the council sanctions a change of policy then people would have to reconsider, and decide whether they would be loyal to the new policy," said one Assembly member still opposed to the package. But for him and a number of others, the emerging bottom line is that "Trimble must ensure there is a party left at the end of all this."

This is where everything begins to impinge on Mr Trimble's own position. While the detailed content is still awaited, it is highly unlikely that the IRA and Sinn Fein statements will contain a specific promise of any decommissioning event within anything the UUP might recognise as a schedule prescribed by Gen de Chastelain.

The qualitative advance on July appears to rest on Mr Trimble's own revised assessment of the republican leadership's intentions. "Having had all this time to look into the whites of their eyes has made all the difference," is how one insider puts it. So, Mr Trimble in effect is expected to ask his party to trust his belief that, given the appointment of the executive, a start to decommissioning will follow within two months.

"But what if it doesn't?" demands one sceptic: "What if we take the risk, cross the Rubicon and get to the end of January only to discover they're still not ready to follow?"

ONE well-placed source says that last Thursday night Mr Trimble had "a fairly clinical appreciation of the realities of his position should the party refuse to support him." The reality being confronted was that the UUP leader would have little further credibility as a deal-maker, if he again failed to deliver his party.

The implicit, but not yet explicit, suggestion in the gathering internal debate is that the same rules would apply should the party decide to gamble on Mr Trimble's new-found trust in the Sinn Fein leadership, only to discover it had after all been misplaced.

But we move ahead of the game. To be sure of winning the breathing space necessary to see his judgment confirmed, Mr Trimble needs to extend a base which currently looks too narrowly confined to his Assembly party, and conspicuously lacks weight.

The assumption is that Mr Ken Maginnis, with little evident enthusiasm, will stick with him. Which leaves the question mark over Mr Taylor and Mr Donaldson. These two men make the qualitative difference to the opposition now lining up against Mr Trimble - enough, sources close to them believe, to bring the party leader down.

Mr Taylor was still on the inside track, when Mr Donaldson faced alone the full barrage of a Downing Street charm offensive designed to win him round in the vital days leading to last year's referendum. That will be as nothing to the pressures both men will face in the 12 long days ahead.