There is no Plan B. That is the stark and loud message which has come through from both the Taoiseach and the Northern Ireland Secretary, Mo Mowlam. It isn't quite true. If the Belfast Agreement collapses on decommissioning, there will be a return to direct rule with a substantially increased input from the Irish Government. Many of the reforms which are integral to the accord will proceed.
But the real prize - a system of genuine power-sharing government in Belfast and a new relationship between this State and Northern Ireland - will be lost.
The Taoiseach has urged all the parties involved not to "talk up a crisis". Mr Ahern has pointed to the progress that has been made since the agreement was signed less than a year ago.
Even in the euphoria of last Good Friday, it would have been very hard to anticipate we would see the signing of a formal treaty setting up cross-Border bodies which, if allowed to work, will lead to much closer co-operation between the two parts of the island.
The decommissioning quarrel is a hangover from the past but no less threatening because of that. It could still destroy all that has been achieved. There is a tendency in some quarters to look on both sides with impatience, as though each is being wilfully stubborn.
Why can unionists not accept the guns are silent and the IRA ceasefire is for real, particularly since the agreement itself does not require the hand-over of weapons as a precondition for Sinn Fein taking seats on an executive?
On the other hand, how is it that the republican movement refuses to see that the spirit of the accord demands a gesture to reassure unionists that the violence is over for good?
Beneath these eminently reasonable arguments there lies the deep mistrust which has always been at the heart of the challenge to find a settlement. The agreement was designed to try to reconcile two opposing visions of the future.
It had to reassure unionists that Northern Ireland's place within the United Kingdom would no longer be under threat, either from the territorial claim of the Irish Constitution or IRA violence.
Sinn Fein needed to be able to tell its supporters that the agreement would leave the way open for political methods to achieve a united Ireland, something which violence had signally failed to do.
A number of opinion polls conducted recently in Northern Ireland cast an interesting light on these large issues. A survey carried out by the Institute of Irish Studies at Queen's University found an overwhelming majority (93 per cent) of people in Northern Ireland want the Belfast Agreement to work.
The overall figure is striking because it must feed through to the political leaders as reflecting a deep and widespread yearning for peace and stability.
But people are more divided as to where the agreement is leading. The opinion poll carried out for the BBC's Hearts and Minds programme last week grabbed the headlines because it showed a decline in support for the accord among unionists. Fifty-five per cent of unionists voted "Yes" in last May's referendum. If there were to be a rerun today, only 4l per cent would do so.
The response to another question goes a long way to explain their disillusionment. When asked "Do you think Northern Ireland will be part of the United Kingdom in 2020?", 51 per cent of those questioned replied "Yes" and 48 per cent "No".
There has been a steady decrease in the percentage of those who believe Northern Ireland is destined to remain part of the Union, from 61 per cent in l997 to 51 per cent today. This decline in confidence in the continuing integrity of the UK is particularly striking among unionists. Just two years ago, 72 per cent of unionists believed Northern Ireland would continue to remain linked to the rest of the UK. Now that figure is reduced to 61 per cent.
Political leaders are fond of saying opinion polls are only a snapshot of what people think at one moment in time. But these figures must prompt serious assessment in Sinn Fein. They seem to indicate that the Adams/McGuinness strategy of working towards a united Ireland by political means is already yielding results.
Unionists may not like the idea of a break with the UK, but increasingly they accept the likelihood of this happening. This should strengthen Sinn Fein's hand with its own dissidents.
We have been told of the serious danger of a new split among republicans on decommissioning, and even of threats to the life of Gerry Adams. My own impression, after talks with Sinn Fein sources, is that there is a profound mistrust of the whole peace process at grassroots level.
It isn't simply that decommissioning is seen as representing surrender by the IRA. There is also a deep suspicion that, from the very start, the peace process has been a plot engineered by the British government (possibly with Dublin help) to lure Sinn Fein into mainstream politics, thereby weakening the IRA to the point where it is no longer capable of operating an effective armed campaign.
The focus on decommissioning has greatly exacerbated these suspicions, as has the perceived failure by the British - and Irish - governments to "face down" the unionists on the issue.
I stress that I am simply reporting what has been said to me. I readily concede that this view of what has happened takes no account of the enormous progress which has already been made on many issues, or of the serious difficulties which now face David Trimble. Again, recent opinion polls point these up very starkly.
This is due, at least in part, to the fact that Mr Adams and his colleagues have preferred to concentrate on the perceived bad faith of most of the other parties to the agreement, rather than to highlight the gains Sinn Fein has made, both at a political level and on the equality agenda.
The same accusation can be made, of course, against David Trimble. The Ulster Unionist Party leader rarely recognises publicly that concessions have also been made by the republican movement. But over the past year the unionist community has had to accept enormous changes and has done so, on the whole, with a new sense of realism and considerable dignity.
There has been nothing like the protest that one might have expected over, for example, this week's treaty setting up cross-Border bodies. Perhaps it is time for Sinn Fein to recognise how fast the tide is flowing in its direction and to make a suitably generous gesture by way of response.