David Trimble intends to give a forceful speech avoiding the empty boosterism so typical of leadership speeches at party conferences.
He wishes to focus, instead, on harsh reality. But the harshest reality of all is that his position, weakened after South Antrim, has weakened since.
Every day seems to bring bad news that he cannot control. A week ago the British government appeared to expend chips on the IRA fugitive issue and demilitarisation in order to win another confidence-building measure on weapons - an IRA arms inspection - which would, in fact, even if delivered, not take the necessary trick of swinging Ulster Unionist votes.
Such is the operation of the law of diminishing returns in politics. Everyone knows that if the agreement survives in the medium term, there will have to be further inspections - few will be much impressed by one in the next few days or weeks. But why is the agreement under threat?
There is an uneasy, sour public mood. On Thursday Victor Barker, whose young child was murdered at Omagh, denounced the Secretary of State for his offhand treatment of his concerns. The Northern Ireland unionist community listening to Mr Barker's dignified complaint will have had in its mind the revolving door which seems to them to exist in Downing Street for those grieving nationalist families who have complaints about police and security.
In the background all the time is the Patten controversy. If various politicians mean what they say, then some grim conclusions can be reached about the Patten report. Sadly, we can now rule out success; the noble Patten vision of a widely accepted police force co-existing with devolved power-sharing institutions appears to be a mirage.
However, were David Trimble to fall quickly, a certain outcome would be the implementation of all those elements of Patten desired by nationalism that can be implemented in the absence of devolution.
The most tragic outcome, and unfortunately the most likely, is that the Patten report will be seen by future historians as the document that killed off the agreement, and did so by fatally undermining the necessary level of Protestant support.
Unionist canvassers in South Antrim reported that Patten was the "killer issue" that elected Willie McCrea and brought about the crisis over David Trimble's leadership. By a heavy irony, those who believe Patten deserves a decent place in history ought now to be rooting for the survival of David Trimble, one of its sharpest critics.
Quite understandably, many outside Northern Ireland cannot understand the difficulty. What can be wrong with Chris Patten's attempts to establish a more widely acceptable police force? Surely the only grounds for objection must be bigotry? But here's the rub. While many unionists now regret the past rigidity of their political leadership, there is no such communal burden of guilt about the role of the RUC during the Troubles.
There is instead widespread admiration for their professionalism and restraint, causing only 52 of the fatal casualties of the Troubles while the republican total stands at 2,139.
The perceived snub to that force embodied in Patten has convinced all too many people that there is something wrong in the value system of the agreement with which it is so intimately associated.
However, let us suppose Mr Trimble somehow survives, maintains his policy and effectively stops the negative passions unleashed by Patten from killing the agreement. What then?
Then Peter Mandelson is committed to an implementation of Patten which he regards as a fair summation of the report but which mainstream nationalist Ireland emphatically does not. Again and again in recent weeks Mr Mandelson has warned against nationalist maximalism on the issue, but has received no response from the SDLP.
The British government is reduced to hoping that Bertie Ahern will decide to staunch the bleeding and, in effect, co-ordinate a compromise. If that does not happen, the SDLP will not offer its formal support to the new structures of policing. Patten's best intentions will have been stymied.
Many unionists will be furious at the suggestion that a party in government can withhold support from the police. Worse still, from a British government point of view, all the pain of Patten on the Protestant side will have been endured for no gain on the Catholic side. Grim times indeed in Belfast when there are political insiders to be found who note that this is not the worst possible outcome.
This morning Mr Trimble has only one real card, his courage. He has to do whatever it is that can be done by sheer force of argument and of character.
His enemies within unionism sneer that he has made numerous mistakes in negotiation, mistakes they would not have made, but the reality is that what is for many Mr Trimble's most significant error - not seeking a deal under the Tories - was replicated by most of his present-day unionist opponents, some of whom privately acknowledged that they wish they had trusted the Tories more.
Amazingly, in the 1994-1997 era there were even senior anti-agreement politicians who appeared to believe that Senator George Mitchell had a tougher position on decommissioning than John Major.
What defines Trimble's position as against that of his enemies within unionism is not that he has made mistakes, and that they - from the vantage point of pure Orange theory - have not, but that he has the courage to challenge his own people to engage with nationalism as part of a strategy to revitalise Northern Ireland's place within the Union.
Today he needs not so much to make the general case for the agreement but rather to reconnect with the emotions in the centre ground of his own party - confused, buffeted and demoralised as it is - and convince them that he is the only leader who can give them the Northern Ireland they wish to see; a Northern Ireland that has left paramilitarism behind.
To do that he has to convince them that he has a bottom line on decommissioning, a bottom line as firm as it was when he forced Peter Mandelson to suspend the Executive on that issue in February.
Losing David Trimble means losing the agreement, which means increased instability, which, on previous form, means increased toleration for loyalist and republican violence.
But it may be that the ethos of New Labour (pragmatic yes, but also lacking in a sense of history and deeply suspicious of British state wrongdoing) has simply left it unsuited to manage Northern Ireland. If one is quizzical about one's own Britishness, it is hard to identify with the passionate imagined Britishness of others who do not even live on the British "mainland".
As he watches the Trimbleistas limber up for yet another battle, which may be their last, Peter Mandelson must be aware that they may not be able to save themselves on their own. This week he has appealed for compromise on all sides.
Mr Mandelson must also be aware, however, that if he has been disappointed by Dublin's level of support for David Trimble, why should he then expect the IRA to ride to the rescue, even if Mr Adams secretly wanted to?
The implication is clear. It is only by a broader and more strategic series of interventions by her majesty's government itself that the agreement can be saved.
Paul Bew is professor of politics at Queen's University, Belfast