David Trimble has appealed to nationalists in Northern Ireland to vote tactically in the British general election next month. In an interview in last Sunday's Observer, the UUP leader argued that, in a number of key constituencies, nationalist voters have it in their gift to ensure the election of pro-agreement unionists - and the defeat of high-profile candidates known to be opposed to the Belfast deal.
Mr Trimble pointed out that even Peter Robinson could be unseated in East Belfast, if the 26 per cent of voters who plumped for Alliance and the SDLP in the 1997 election switched their support to the UUP candidate. He added: "Imagine what Ulster politics would be like if Peter Robinson lost his seat."
This is almost certainly wishful thinking. For Peter Robinson to lose his seat would be a political upset comparable to the defeat of Michael Portillo in New Labour's sweep to power in 1997.
The deputy leader of the DUP has represented East Belfast, as he himself put it recently, for "decades and decades". He has been a popular local representative and an extremely effective minister in the executive.
But there are solidly unionist constituencies, where tactical voting by nationalists could lead to the election of a pro-agreement candidate. The most obvious is Bob McCartney's seat in North Down. The constituency is the most prosperous in Northern Ireland.
It is not unreasonable to suppose that there is a majority which has benefited from the Belfast Agreement and the economic opportunities which have flowed from it. It is also clear, from the figures at the 1997 election, that even a relatively small switch in allegiance by Alliance and SDLP voters could give the seat to Lady Sylvia Hermon, the UUP candidate.
The waters have been muddied in North Down by the successful bid to prevent Peter Weir, who is opposed tooth and nail to the agreement, from contesting the seat for the UUP. But there is also a much larger question mark as to whether Northern Ireland's electorate is ready for the kind of seismic shift which the use of tactical voting would represent. Past experience has shown that the voters, on both sides, find it extremely difficult to break away from traditional tribal patterns.
On this occasion, David Trimble has not made it any easier for nationalists who might be prepared to consider helping him out at the ballot box by putting IRA decommissioning back on the agenda. This may have been necessary to unite his own party but, inevitably, it has irritated moderate nationalists who support the agreement. They believe that the deal has delivered a relatively solid peace, brought former paramilitaries into the political process and that the new political structures are working well. They fear that the unionists' obsession with IRA decommissioning could put all this at risk.
Mr Trimble's first task must be to try to convince those unionists who came out to vote in favour of the Belfast Agreement in 1998 that it is in their interests to vote for his party's candidates. His announcement that he intends to resign as First Minister on July 1st unless there is progress on the weapons issue is aimed at those in his own community who feel that concessions on too many issues - the release of prisoners, reform of the RUC, etc - have already been made to Sinn Fein. But the unionist leader has also been careful to emphasise that he would not expect his resignation, should it take place, to be followed by a walkout by UUP ministers from the executive. On the contrary, he believes that they would remain at their posts and that the power-sharing executive would survive.
David Trimble's post-dated letter of resignation has been dismissed by his critics as an election stunt. It would be unwise to take it too lightly. It has always been one of the UUP leader's great strengths that he clearly believes that there is life beyond politics. It may be he has already decided that, if the forthcoming election goes badly against him, he would prefer to walk away from Northern Ireland's tortuous quarrels. When Mr Trimble was elected leader of the UUP, the general reaction of liberal commentators was one of dismay. Given his track record, it was assumed that he would impede all political progress towards an inclusive settlement. Instead, he has grown in stature with every crisis he has had to overcome, inside and outside his own party. He is entitled to claim that, since the Good Friday agreement was signed, he has worked as hard as any politician on the nationalist side to make it work.
If David Trimble does resign in July, the agreement will survive. But it will be plunged into another period of crisis. A great deal of the progress that has been made on bread and butter issues as a result of devolution will be put at risk. International confidence in the Executive and the political structures set up under the accord will be eroded. Whatever happens in the longer term about decommissioning, David Trimble needs to do well in this election if such a crisis is to be averted. Nationalists in constituencies such as Strangford and North Down will have to think carefully about the value of their votes.