This weekend the situation in Northern Ireland enters its most serious crisis since the Good Friday Agreement three years ago. It is universally accepted now that David Trimble will carry out his threat to resign as First Minister, because the only thing that would prevent him would be a new move towards disarmament by the IRA, and the IRA does not want to appear to be acting under pressure from the Unionist leader.
Quite suddenly, politics in Northern Ireland may be moving into a new, post-Trimble phase. It seems that the Nobel Peace prize-winning leader of the Ulster Unionist Party really is coming to the end of the road. He has led representatives of a majority of the reluctant and suspicious unionist population into a power-sharing Assembly that is genuinely historic. It was part of a process which saw the IRA take the first small step towards decommissioning its arsenal.
Yet he is right to feel that he has been betrayed by the republicans – or, if not he personally, that the peace process has been betrayed by Sinn Fein and the IRA. Opening a few weapons hoards to independent inspection was important, but it could only be the start of a process – a process which was supposed to end, not begin, in May last year.
It is tragic yet understandable, therefore, if Mr Trimble has decided he has done what he can and that he is entitled to leave it to others to try to find a new way forward. It means there will be a dangerous vacuum where the leadership of moderate unionism should be at a time of high tension on the streets of Northern Ireland, with riots in Belfast even before the marching season begins.
It should be clear, however, where responsibility lies. Sinn Fein's leaders have had an erratic relationship with the truth, but Gerry Adams' insistence, repeated yesterday, that the current crisis had been precipitated by Mr Trimble's resignation threat, is particularly empty. The main blame for the crisis lies with the republicans for their failure to deliver on the promises they made in the Good Friday Agreement.
There are several reasons for being reasonably optimistic about the outlook for Northern Ireland over the medium- to long-term. The pressure of their fundamental interests should still be forcing the republicans to keep the institutions of the Good Friday Agreement alive. The Assembly and the all-Ireland bodies give them a say and a public standing they would not have without them. The reforms of policing and the winding-down of the British military presence are what the nationalists have wanted for a long time.
On the unionist side, there are signs that the leading opponents of the Good Friday Agreement – including, significantly, Jeffrey Donaldson, who is a candidate to succeed Mr Trimble – have softened their position. There seems a wider acceptance, even among Ian Paisley's Democratic Unionists, that the Northern Ireland Assembly should survive.
What is difficult to see, however, is how Northern Ireland gets through the next few weeks. It seems that the 10 ministers who make up the executive can carry on their day-to-day business without a First Minister. There will be much talk of suspending the Assembly, of trying to avoid new elections to the Assembly, in which Mr Trimble's party would be expected to do badly, of setting new deadlines for agreement. There may be speculation about a change of leadership of the Ulster Unionist Party, and the fact that Mr Donaldson is not a member of the Assembly.
Through all this, however, it is vital not to lose sight of the fact that the next step must come from the republicans and that, until the IRA puts some of its weapons beyond use, no leader of the Ulster Unionists can persuade the unionist people that the peace process is in their interests too.