For a long time now, unionists have been inclined to assume the worst. Faced with any change, they have tended, often for good reasons, to ask "where could it lead?", "what can go wrong?". At times, that habit of mind has been a barrier to progress. Right now, it ought to make progress possible. For if those questions are asked calmly and clearly, unionists must realise that the worst that can happen if they accept the deal on offer from the British and Irish governments is not so bad. Suppose for a moment that all their fears are completely justified. The two governments have been either fooled or bullied into going along with a cruel deception. The IRA has no intention of getting rid of its weapons. Sinn Fein is using weasel words to lure David Trimble into allowing it into government. When the executive is formed, the issue of arms will disappear yet again into a morass of equivocation and evasion. If all of that is true, then the deal on offer still has one overwhelming attraction. We will all know the truth in about two months' time.

If the Ulster Unionist Party takes the deal, even under protest, and allows the executive to be formed, the republican bluff (if it is a bluff) will be called. The nature of the problem will be entirely clear to everyone: the IRA does not intend to go away. There is, moreover, a further attraction for unionists. They don't have to believe the assurances of Sinn Fein, of Bertie Ahern or even of Tony Blair. They can enter the executive under protest, with all their reservations intact. They can say, in effect: "This is a terrible deal, a rotten betrayal of the unionist constituency. And we're going into the executive to prove, once and for all, just how rotten it is." If they do that, there are two possibilities. Either they are proved right: Sinn Fein falls back on double-speak and the IRA doesn't engage in the disarmament process to the satisfaction of the de Chastelain commission. Or they are proved wrong: the process begins in earnest within weeks and the IRA has effectively dissolved itself by May 2000.

In either event, the unionists win. The first scenario may be extremely unpleasant, marking as it would the collapse of the peace process. But the UUP would emerge in a very strong position. David Trimble's prestige would be immensely enhanced. The two governments would have to try to construct a new settlement from which the republicans would be excluded, unless and until the IRA began to disarm. In the second, more benign scenario, the UUP might lose some face but it would gain an extraordinary prize: the end of the IRA. Mr Trimble and his colleagues would have proved to be rather too suspicious. But who, in the happy event of a functioning peace settlement and the removal of the gun from Irish politics, would want to rub it in? In the internal struggle within unionism, moreover, the UUP's position would be greatly strengthened. Mr Trimble's willingness to take risks would have been justified beyond argument. What, then, of the issues of principle? Many unionists are genuinely and sincerely disgusted by the provision in the deal for the executive to be collapsed if the IRA does not live up to its responsibilities. This, they point out, makes the very existence a democratic administration dependent on the actions of a private army. In one sense, this objection is so clearly true as to be unanswerable. It is indeed appalling that the IRA holds an effective veto over the progress of a democratic settlement. But that is precisely the situation in which we have been for the last 30 years.

Time and again, the paramilitary gangs on both sides have wrecked political settlements. That power is not given to them by last week's agreement but by the brutal fact that an armed gang with a sufficient political base can always undermine a democratic society. Joining the executive, even under protest and in the stated expectation of failure, turns a situation in which unionists cannot win into one in which they cannot lose. The responsibility of all those who want the peace process to work is to allow them to reflect in the kind of atmosphere that makes it possible for them to see that. Nationalists should try, even for a moment, to look at the problem from a unionist perspective. From that point of view, the whole decommissioning business has been the subject of an apparently infinite process of postponement. In Patrick Mayhew's fateful formulation in Washington in March 1995, the "actual decommissioning of some arms" was meant to "signal the start of a process", allowing Sinn Fein to take its place at all-party negotiations. In January 1996 the Mitchell report recommended that "some decommissioning would take place during the process of all-party negotiations". But, as we know, decommissioning happened neither before nor during the talks. It is not paranoid to believe that it won't happen after the talks either.

Nor has Sinn Fein done much to help. In fact, the party has deliberately set out to arouse sectarian animosities over the arms issue by repeatedly alleging that Mr Trimble and his colleagues are using decommissioning as a mere cover for atavistic bigotry. Yet again, in yesterday's Irish Times, Gerry Adams claimed that "the rejection by the UUP of the Sinn Fein initiative . . . is yet more evidence that for many unionists the real problem is their refusal to share power with Catholics. To quote one, they `don't want to see a Fenian about the place'. " Just consider this statement for a moment. Anyone reading it would understand from the context that a member of the UUP engaged in last week's talks had made a statement about not wanting "to see a Fenian about the place". And if this was indeed the case, then it would be perfectly reasonable to suggest that unionists are merely using the arms issue as an excuse. But when did a unionist make this statement?

The strict answer is never. The broad answer is July 12th, 1932. Mr Adams, presumably, is thinking of a notorious speech by Sir Basil Brooke on that date when he remarked that he "had not a Roman Catholic about his place". By reaching back 67 years, and falsely ascribing Basil Brooke's vicious bigotry to the present leadership of the UUP, the Sinn Fein president is deliberately painting the whole issue of what happens to IRA arms as a mere product of rabid Protestant sectarianism, not worthy of serious consideration. Is it any wonder that the UUP (which, incidentally, has been anxious to share power with the largely Catholic SDLP for most of the last decade) is so deeply suspicious? Instead of deploying this kind of rhetoric, the republican movement should be taking seriously its declared intention to "make space" for the unionists. Space is made by clearing away the old junk, not by dragging it back in. Instead of having to fend off insults, or being urged to make a "leap of faith", unionists should be allowed to think coldly and calmly about their own interests. By considering the worst, they should be able to act for the best.