In February 1951, Sir Basil Brooke, then the prime minister of Northern Ireland, addressed the Ulster Unionist Council. His message was an uncompromising one: unionism faced with a Labour government at Westminster had to modernise, move away from discriminatory practices or find a new leader.
In his diary, Brooke recorded: "I told them that the Convention on Human Rights compelled us to be fair to the minority, that I was not going to be responsible for discrimination.
"I finished off by saying that if they wanted another administration who could perhaps solve these domestic problems from a new point of view, and if they thought we were not handling the socialist government right and wanted a government which would discriminate [against] Catholics, they could do so. I would not take on the job."
Brooke's approach helps to explain the otherwise inexplicable: his good relationship with senior socialists, like Herbert Morrison, a key cabinet figure and Peter Mandelson's grandfather.
Today, though David Trimble has resolutely refused the demagogy of "back me or sack me", he may well feel the same way. Does anyone in the Ulster Unionist Party have a better way of handling the Labour government?
Trimble is a proud man. It was difficult work behind the scenes to persuade him not to resign as First Minister in the aftermath of Seamus Mallon's resignation as Deputy First Minister, even though that might well have finished the agreement there and then, as it was unlikely there were enough unionist assembly votes to place him back in office.
If he loses today, many will try to persuade him to stay on, pick up the pieces and salvage whatever can be salvaged.
They will have their arguments. Some Unionist delegates who feel betrayed by Tony Blair still feel that Trimble is the best leader they have. Trimble is felt by some to lack the personal touch but he is not as hated as Brian Faulkner was at the end of 1974. However, Trimble himself may well feel he has had enough - and with him, Ulster Unionists would lose the first leader it has generated in the course of the Troubles who has real credibility and respect within mainstream British public opinion.
Politically, David Trimble has had two great obsessions in the two years since the agreement was negotiated. One was the all-consuming game of high politics; negotiations involving Bill Clinton, Tony Blair and Bertie Ahern, Gerry Adams and Seamus Mallon, which took up so much of his time, leading to a neglect of such crucial matters as internal party reform. This is a neglect which may yet prove fatal if the block votes of the Orange Order and the rather more passionately anti-Trimble Young Unionists defeat him today.
The other great obsession was with the constitutional meaning of the agreement he had brokered: for Trimble it means above all that nationalist Ireland accepted the legitimacy of the Union in exchange for a new deal on power-sharing and a North-South dimension.
Trimble's analysis of the constitutional meaning of the agreement is the clue to his current approach to the crisis. He is quite genuine in his belief that the Patten report's attitude towards British state symbolism is in conflict with the agreement.
He is equally genuine in his belief that Sinn Fein ministers hauling down the Union flag in their departments is in conflict with the agreement. During a prolonged dialogue over several months, he had some considerable success in alerting Peter Mandelson to his difficulties and indeed, some success in winning Mandelson over to his analysis.
Mandelson's clashes with Brian Cowen on this point - so memorably captured in the leaked British memorandum on the subject - became increasingly sharp from the beginning of March and gradually exploded into full public view at the end of April. As the Secretary of State put it this week: nationalists have to give more than lip service to the legitimacy of Northern Ireland's position in the United Kingdom.
But here is the rub. Many ordinary Unionists have little interest in Trimble's constitutional niceties. They do not like the Patten report's recommendations, not because it is incompatible with Trimble's interpretation of the agreement; they do not like it because they think it tends to legitimise terrorism against the forces of law and order.
They did not like the behaviour of Sinn Fein ministers - not because it was incompatible with Trimble's interpretation of the agreement but because they found it sectarian, "in your face", undemocratic and a recipe for instability.
This is the clue to the recent failure of the unionist community to respond more warmly to the IRA statement, which genuinely broke new ground - a failure which surprised David Trim ble himself and helps to explain his uncharacteristic hesitancy - now banished decisively in the last days of the campaign.
The weakness of the Trimble campaign, despite his numerous impressive media performances which made his opponents look mediocre and incoherent, was a reluctance to face up to this fact.
He controlled the argument on decommissioning: dumping, followed by inspection, is decommissioning by another name. He was helped by the government's many proposed changes to Patten, but he failed to counter unhappy memories of devolution in practice.
The Trimbleistas shrugged when pressed about the experience of the working Executive - "a deal is a deal" - and they add that if the Unionist political class was not so divided, the party would have six ministers, instead of the four now promised if, as seems possible, the DUP withdraws from the executive.
They add that Bairbre de Brun's controversial decision to favour West Belfast maternity services over those of South Belfast was probably going to come from the direct rule administration anyway. One thing is clear, as one Stormont insider put it: "There is no point in giving Sinn Fein 60 per cent of the budget and then complaining when they begin to spend it."
More encouragingly, it is clear that the period of suspension has not been wasted - serious work has gone on which means that for the first time in 30 years, the Ulster Unionist Party is equipped with developed policies on important matters of public policy.
Nevertheless, there has been a visceral Protestant reaction to Sinn Fein's possession of departments which touch so tangibly the lives of so many citizens. Jeffrey Donaldson was only ever effective when he slipped in the line about his two young children coming under the care of Martin McGuinness; the collective communal shudder was palpable.
This is the issue which above all hurt the Trimble campaign. Only late in the day was it addressed with conviction - in the leadership's letter to delegates and Trimble's interview in this newspaper with Frank Millar on the eve of the meeting. The case, in essence, was simply this: unless a more consensual style of Executive work evolves, ministers will find themselves hamstrung forever on their key legislative projects.
As that reality began to sink in, the Trimbleistas believe that more consensual style was genuinely evolving before the fall of the Executive but if they are wrong, the tides of protest - beginning with the South Antrim election and culminating in the general election - will destroy pro-agreement unionism and with it the agreement, even if Trimble carries the day today.
We can now be sure of only one thing about today's vote - it is not the last crisis of the peace process. Whether in or out of the Executive, the DUP intends to keep up the pressure until, at least, the next general election. Council by-election results so far suggest that it has an alienated public opinion tending towards its view of things.
If Trimble finally runs out of luck - and worryingly, he has been incredibly lucky so far - what is lost? The Belfast Agreement? Trimble's own leadership? The whole project of new unionism?
Quite conceivably all these disasters are just around the corner, but Trimble has one card. The 860 delegates who meet today have the decisive say. Every time they turn on the radio or the TV, they are told this and it is true. If they vote Yes, Trimble can guarantee that their influence will be maintained and they will be back to review progress or protest against the lack of it.
But if they vote No, this might be the last really important meeting of the Ulster Unionist Council; in short, it might well be the end of that organisation's profound and shaping influence on Northern Ireland's politics.
Paul Bew is professor of politics at Queen's University, Belfast