The see-saw nature of Northern Ireland politics was rarely so clearly evident as during the past week. Last weekend saw David Trimble down, Sinn Fein up. But what Tony Blair gives with one hand, he takes away with the other.

He may have pucked Trimble in the wind with his Downing Street Draft and the subsequent declaration that June 30th was an "absolute" deadline for devolution, but on Monday his chief of staff, Jonathan Powell, sent Mr Trimble a letter of comfort, taking the sting out of the weekend's events and providing the UUP leader with political cover against the doubts and criticism of his Assembly members.

There was consternation in unionist ranks over the draft prepared by Downing Street on the evening of Friday, May 14th. Sources say John Taylor departed about 4 p.m. to try to get a flight home but, in the event, was unable to travel until the following morning, when he flew on the same plane as David Trimble.

The fateful draft began to take shape after Mr Taylor's departure and it seems Mr Blair was at his most persuasive with the UUP leader.

Trimble brought the document home to his Assembly party the following morning. Reaction was swift and angry. Only the more academic members of the party had a good word to say about the document. Trimble was in trouble.

Republicans, meanwhile, must have felt like chortling. To all intents and purposes they had upended the Hillsborough Declaration; the obdurate stance of the IRA on decommissioning had worked; and now the two prime ministers were putting the Ulster Unionists under the hammer.

There was unionist puzzlement and concern at the about-face by Mr Blair. Observers believe the change - which was also executed by Bertie Ahern - reflected the pragmatic approach to politics favoured by both government leaders.

In Mr Blair's case there was probably also a "Kosovo Factor". The war in the Balkans has not been going terribly well from London's point of view, and some good news on Northern Ireland would be welcome, especially if it made Mr Blair look like a peacemaker again.

Call it cynicism, call it realpolitik, but that's the way the world works. It has been a feature of the governments' approach to this process that they lean towards the unionists at one point, then towards the nationalists, and finally end up plotting a course between.

From the Taoiseach's Sunday Times interview of February 14th to the Hillsborough Declaration on April 1st, it was all going Mr Trimble's way. Then the hard men and women on the republican side dug their heels in - can't disarm, won't disarm. It was back to the drawing-board for Blair and Ahern. If in doubt, reach for Gen de Chastelain and his decommissioning body. He is now scheduled to make the report that will probably, once and for all, decide the fate of the peace process.

That report may not be ready until the end of June but, in the meantime, preparations are under way to secure the nomination of ministers in accordance with the d'Hondt system of proportionality.

It is understood the governments want to secure these nominations by the first week in June. Mr Trimble will be away next week and is expected back in Stormont on June 1st.

The attempt to run d'Hondt in the Assembly will tell a tale. The Powell letter (which would presumably have been prepared in the closest consultation with his boss) appears at first glance to offer Mr Trimble a pledge that Assembly standing orders would be changed so the ministers would only be ministers in name, would not even have "shadow" status, and their nominations would automatically lapse if devolution failed to occur by June 30th.

But the version being leaked by pro-Trimble sources did not include the significant qualification that any such change in standing orders on the part of the Secretary of State would be "subject to the views of other Assembly parties".

The text of the relevant paragraph is: "Incidentally, as you know, you said quite clearly to all concerned on Friday evening that you did not intend to call a shadow executive meeting. Subject to the views of other Assembly parties we would be prepared to amend the standing orders on the lines discussed at Hillsborough so that they would refer to `those to take up office as ministers when powers are devolved' and that nominations would come to an end on June 30th if devolution had not occurred by that date."

While the full text of this key paragraph does contain the comforting qualifier about consulting other parties, republicans are concerned about its implications. They are somewhat alarmed that, only two days after Mr Blair had laid down an "absolute" deadline for devolution, a letter in the name of his chief of staff was setting out a formula, however conditional, which played into unionist hands.

The naming of Martin McGuinness and Bairbre de Brun as Sinn Fein candidates for ministerial office at the party's ardfheis showed how important it was for Sinn Fein to move forward and take up its places in government. Unionists have been trying to put a brake on that process, pending IRA decommissioning.

But there are attractions now for unionists in having the new cabinet named. Once that has been done, the focus will shift to Gen de Chastelain's report and his consultations with the parties, and perhaps even with the paramilitaries themselves.

The theory goes that the pressure will be taken off the UUP leadership and placed, where unionists believe it rightly belongs, on the shoulders of Gerry Adams and Martin McGuinness. Can they persuade the IRA to "do the decent thing" on weapons at long last so that the executive can be formed and devolution proceed in tandem with Scotland and Wales?

Gerry Adams may come to regret suggesting in Washington that he and David Trimble should "jump together". This has been seized on by the unionists to effectively mean they would agree to be more flexible about the timing for getting rid of weapons provided they had an absolute guarantee that the guns would be destroyed.

There is no convincing evidence that the IRA has any intention of giving up weapons. Senior Sinn Fein spokesmen have said privately the IRA did not intend to call a ceasefire either, so decommissioning in the long term could not be ruled out. No experienced observer expects guns by June 30th but there will be an attempt to tie the IRA down to destroying weapons by the May 2000 deadline set in the Belfast Agreement.

The Mallon plan for expelling Sinn Fein if decommissioning did not take place by then is still on the table. Implementing it would have great difficulties for the SDLP: the two governments would have to play the major part as they did in the expulsion of Sinn Fein from the talks at Dublin Castle last year. Unionists will be reading the small print of the Mallon plan if it ever becomes part of a formal agreement.

"You will get IRA movement if Sinn Fein is in government," senior nationalist sources predicted confidently last night. Other sources, close to the republican heartland, are not so sure. David Trimble is being asked to make a leap of faith but then, in the immortal words of Albert Reynolds: "Who's afraid to take risks for peace?"