Is David Trimble now following the same path as Mikhail Gorbachev, his fellow Nobel laureate? Is he a leader who did all the right things for all the best possible reasons but succeeded only in smashing up his party, which had been the party of the state, leaving it in possession only of its most marginalised heart-lands?

The prospect of the Ulster Unionist Party shorn of its best people going the same way as the Communist Party of the Soviet Union transfixes the collective political imagination at this dangerous and decisive juncture.

Let there be no illusion about this: in the absence of a definitive IRA promise to decommission rapidly following the formation of an executive, David Trimble faces an almost impossible task in containing the emotional and ultimately self-destructive urges within his own party.

As one senior SDLP figure noted at the weekend, the Sinn Fein leadership refused to ask for a ceasefire until they were sure of a result; Mr Trimble is being asked to get his people to make a major move when, to say the least, he cannot be sure of the result.

But the story of the period since the agreement was signed has been, to a large degree, the story of the political incompetence of No unionism, and of Mr Trimble's amazing political luck, a quality which cannot be relied on for ever.

Given numerous opportunities to finish Mr Trimble off, the anti-agreement unionists have fluffed it, but this is their moment of truth. They have steadily strengthened their position within the party structures. Regardless of the details of the Mitchell package, they are able to mobilise emotion on the simple issue of Mr Trimble's alleged "respectabilisation" of the republican leadership.

There is now a wide gap between Mr Trimble's view of the republican leadership and that of the ordinary unionist. The fact that Mr Trimble's view is probably considerably more accurate does not alter his vulnerability on this score. The average grassroots Ulster Unionist Council delegate has no sense of the increasing role which electoral prospects in the Republic now play in Sinn Fein calculations.

If Sinn Fein can present itself as the party which has taken the gun out of Irish politics and at the same time entered government in the North, its prospects in the Republic will receive a further boost, and for a long time now Mr Adams has believed that progress towards Irish unity cannot be based simply on the party's Northern strength.

To survive, Mr Trimble has to present a picture of possible republican calculations which is cold-eyed, stripped of any sense that he has been seduced by any personal warmth in negotiations or that he knows the unknowable, but realistic.

Coupled with this, he has to make it clear, and Mr Trimble has always made this perfectly clear, that while a long-term peaceful competition between republicanism and unionism, played accordingly to the pro-consent ideals of the agreement is fine, the coercive republican message is over.

The message which talked of no decommissioning except the decommissioning of the British state in Ireland must be consigned to the dustbin of history and must be seen by all to be consigned to the dustbin of history.

Mr Trimble is in a position to state that an agreement in which every obligation is fulfilled, except the decommissioning obligation, is not worth having, whatever its other good points, and that rather than smash up his party over the issue he will walk away himself if the republican movement does not live up to its intimations that it will decommission within the next few weeks.

The UUP is in a position whereby if it displays a little patience it can avoid an internal bloodbath from which it will not recover. If Mr Trimble's gamble pays off, and the republicans make the decisive break with their violent past, then everyone will be happy. If Mr Trimble has got it wrong, the sceptics will have their triumph anyway.

Mr Trimble has an advantage in all this. His opponents have visibly no strategy at all to deal with the forces of nationalism, let alone the British and Irish states' self-interest in the matter. Even more importantly, and this is where the analogy with Brian Faulkner's failure in 1974 breaks down, the DUP will nominate ministers to the executive, albeit with a massive show of reluctance, and a new pan-unionism will slowly form.

One of the most able British officials remarked privately in the early days of the peace process that the logic of the pan-nationalism of the Hume-Adams approach was to call into being a new pan-unionism.

I still retained enough of the 1968 mentality to shudder inwardly when I heard this observation, but it remains profoundly true. Either unionism begins to operate with the same degree of unity as nationalism or it can shut up shop and go home.

After his victory in the referendum, that unity has to be on Mr Trimble's basis rather than Dr Paisley's or Lord Molyneaux's, both of whom, by dint of a long period of trial and error, have shown themselves to be easy enough to outmanoeuvre by Anglo-Irish strategy, not to say Northern nationalist strategy.

In the next few days Mr Trimble will need help from the British government amounting to a rebuke of Chris Patten's demagogic sell of his report. The great bulk of the report is sustainable, but Mr Trimble needs help both on substance and symbols. As Mr Patten appeared to have forgotten, the Prime Minister had pledged during the referendum campaign there would be "no local policing"; this is a pledge which will have to be upheld.

Again Mr Patten's idea that the logic of the agreement implied the obliteration of British or Irish symbols needs to be reconsidered, though it goes without saying that the logic of the agreement does imply, not the obliteration of British or Irish symbols, but the greatest sensitivity, one might say understatedness, in their use.

But if the British government helps Mr Trimble in this matter, the Irish Government should help Mr Adams. Any Irish government has immense capacity to make it clear to a Sinn Fein leadership which has decisively rejected violence that it, and Northern nationalism generally, is very welcome within the polity of the Republic. Then let the battle of ideas begin, between the Union as a concept and the Republic as a concept, and long may it be a peaceful one.

Paul Bew is professor of Irish politics at Queen's University Belfast