He and a small number of Unionist politicians - most of whom had, oddly enough, previously been known as hardliners - broke ranks with the Unionist mainstream to suggest a system of "voluntary coalition". Under this modest proposal a Unionist prime minister would invite nationalists into his cabinet and thus, in effect, set up a power-sharing administration.
The idea of having Catholics and nationalists in government was too much for the leadership of Unionism, and when the plan was revealed the wrath of the Rev Ian Paisley and other loyalist leaders was terrible to behold.
Mr Trimble and his associates were denounced, anathematised and pilloried. Although then only a minor figure, he incurred Mr Paisley's particular anger when, speaking at the final session of the Northern Ireland constitutional convention, he closed his speech with the words: "We should look for our brave men in prisons and for the fools among politicians."
White and trembling, Mr Paisley got to his feet to deliver the most extraordinary personal attack on Mr Trimble. When Mr Paisley refused to give way, uproar ensued, with Mr Trimble and his colleagues walking out. They walked out to oblivion: their party, the Vanguard Unionists, split in two and fell apart.
Although Mr Trimble quietly joined the Ulster Unionist Party a few years later, his record told against him. Even though he was obviously one of the party's most articulate and energetic and best-educated members it was not until 1990 that he found a Westminster seat. That done, it took only five years for him to become leader and two more to come to his present dilemma. Once again, he is at the point of choosing between far-reaching negotiation, and aligning his party with the nay-sayers led still by Ian Paisley.
His years in the wilderness must prey on his mind, together with the recognition that Mr Paisley retains the power to savage Unionists who step outside the laager. But he also knows that Unionism looks in need of modernisation, that Tony Blair's peace train is just about to pull out of the station, and that the outside world will not easily forgive his refusal to take part in this determined bid to end the Troubles.
David Trimble is almost a child of those troubles. Born in Belfast in 1944, he was studying law at Queen's University in the late Sixties when some of his fellow students took to the streets as part of the civil rights movement. He took no leading part in events and, having taken a first- class law degree, stayed on at Queen's as a lecturer.
His first foray into politics came in the early Seventies when he joined Vanguard, an unusual entity that was part political party and part attempt to draw some of the splintered shards of loyalism under one umbrella. The irony is that Vanguard's raison d'etre was its belief that the Ulster Unionist Party (which Mr Trimble now leads) was too soft.
Its leader was Bill Craig, a controversial figure who in 1968 had been sacked from his Stormont cabinet post by the reforming Unionist prime minister Terence O'Neill. He seemed to stand for unyielding opposition to the civil rights movement and for a readiness to challenge the British government's authority over Northern Ireland.
Freed from the responsibilities of office, Craig flirted with some loyalist paramilitary organisations including the Ulster Defence Association, which was later declared illegal. Advocating a semi-independent Northern Ireland, he alarmed the authorities in 1972 by staging a series of Oswald Mosley-style "monster rallies", arriving complete with motorcycle outriders to inspect thousands of men drawn up in military-style formation.
What Craig said at the rallies and elsewhere was even more alarming. In a series of what became known as the "shoot-to-kill" speeches, he openly threatened the use of force. He declared: "We must build up dossiers on those men and women in this country who are a menace to this country because one of these days, if and when the politicians fail us, it may be our job to liquidate the enemy."
Addressing a meeting of the Monday Club, he added: "When we say force we mean force. We will only assassinate our enemies as a last, desperate resort when we are denied our democratic rights." Asked if he meant the killing of all Catholics, he replied: "It might not go so far as that but it could go as far as killing."
There were calls for Craig's prosecution: some argued he was giving voice to legitimate Protestant anger while others complained he was fanning the flames of violence. Whether the shoot-to-kill speeches were cause or effect, almost 500 people died that year, the worst death toll of the troubles, as loyalist violence augmented that of the IRA.
While some grainy black-and-white television footage survives showing Mr Trimble perched on the corner of Vanguard platforms, he was in those days a figure too minor to attract attention. And while his leader was making such hair-raising remarks, the newspapers of the time carry no trace of Mr Trimble personally endorsing them. His own contributions of the time tend more to the pedantic than the inflammatory.
Two years later he supported the 1974 loyalist strike during which Protestants, including paramilitants, took over the streets of Northern Ireland in a direct and successful challenge to the power-sharing experiment of the time, and indeed to the overall authority of London.
Emerging from such a background, it was all the more surprising that Craig, with Mr Trimble and others in support, should propose a scheme such as voluntary coalition, which was pretty obviously power-sharing under another name. One of the mysterious little paradoxes of the history of the Troubles, it was the beginning of the end of Craig's career and a severe setback for that of Mr Trimble.
Re-entering the Unionist Party, his career was comparatively quiet until the Anglo-Irish agreement of 1985. All Unionists hated the London-Dublin accord but Mr Trimble, apparently feeling that his party's opposition did not go far enough, became involved in a new organisation, the Ulster Clubs.
The clubs organised street protests and rallies during the tense period of 1985-86, and produced some nice historical ironies. The clubs picketed the office of the Unionist MP John Taylor, who is now Mr Trimble's deputy; they were also scathingly denounced by Ken Maginnis MP, now one of his leadership team.
The Ulster Clubs leader, Alan Wright, employed Craig-like rhetoric: "Faced with treachery as we are today, I cannot see anything other than the Ulster people on the streets prepared to use legitimate force." Mr Trimble said at that time that he had no objection in principle to "mobilisation and citizens' army calls", adding: "I would personally draw the line at terrorism and serious violence. But if we are talking about a campaign that involves demonstrations and so on, then a certain element of violence may be inescapable."
While some may point to this as evidence of irresponsibility, it clearly falls far short of any advocacy of violence. The point must also be made that a trawl through the utterances of a great many Unionist politicians would produce a great many more examples of statements that verge on the dubious which they made at times of crisis and high tension.
But the Irish, north and south, have elephantine political recall, and the Trimble record is there. One veteran observer explained: "People have long memories - they remember Vanguard and the Ulster Clubs and all that, and then they hear him going on about IRA decommissioning and relying on democratic methods alone."
When Harold McCusker died of cancer in 1990, David Trimble was not first choice for the safe seat, but following his election his energy and articulacy made him stand out in a party with notorious communication deficiencies. Even so, he was very much an outsider in the 1995 leadership contest caused by the resignation of James Molyneaux, who was considered by many in the party to have placed too much trust in John Major.
Most believe it was the Drumcree factor that won Mr Trimble the prize, the party opting for the man whose uncompromising stand had helped to get the 1995 Orange march through in the teeth of police and governmental opposition. Since then his party's identification with Orangeism has deepened, as so much attention has remained on the marching issue.
The hectic political scene has meant spending less time with Daphne, his second wife, and their three small children in their modest suburban home not far from Belfast. A former student of his, Daphne describes herself as "the domestic back-up". For recreation he listens to Wagner, Verdi and Strauss.
But the grand sweeps of opera have yet to give him the inspiration to provide the new vision that, Unionists admit, their cause so desperately lacks. Mr Trimble proved effective enough at dealing on a tactical day- to-day basis with a weak Conservative government, but is now being put to the test by a strong Labour administration.
While his career illustrates that he comes from the far right of Unionism, the voluntary coalition episode shows that on at least one occasion he was prepared to contemplate a radical new departure. The last time David Trimble did that he was vanquished by Ian Paisley: this time his choice is between taking on Mr Paisley and taking on Tony Blair. It may be the most critical decision of his entire career, past and future.