So let us start with the man; a lot hangs on him. David Trimble is by far the cleverest, most articulate and energetic Ulster Unionist MP, a star in the greyish and taciturn spectrum of that parliamentary party. He was chosen not only for his flamboyantly unyielding Unionism, exemplified by his clutched-handed stride with Ian Paisley during the Portadown Orange confrontation this year, but also because, quite simply, he is the sharpest native advocate Ulster Unionism has. It has been all too easy to mock Unionism as a tongue-tied, unimaginative, essentially stupid politics; that's going to be harder from now on.
One of the first things that is likely to happen is the swift opening of private talks between Trimble, Peter Robinson of the Democratic Unionists, and Robert McCartney, the recently elected North Down MP. The latter is a hardline but independent Unionist who would be a natural go-between for the two Unionist parties after their two decades of mutual hostility.
Though Trimble has been a long-time advocate of the reunion of the UUP and Paisley's DUP, a merger isn't likely in the short term. Nor would Trimble relish getting into bed with Paisley - and who, let's face it, can blame him? What we should be looking for, though, is the arrival of a de facto Unionist pact led by Trimble, McCartney and (as Paisley eventually fades from the scene) Robinson.
That would change the dynamics. In recent years, ''Unionist politics'' has been almost an oxymoron; as the UUP was outmanoeuvred by John Major and the DUP excluded itself because of its leader's hysterical bellowing, neither party shaped events. In their rhetoric they seemed backward. They had few plausible ideas. Like an army that possesses a nuclear bomb but no soldiers or strategy, they had their ultimate veto, but absolutely nothing else to fight with.
What would this more active, triple-headed Unionism propose instead? None of the men I've mentioned want to give an inch to Dublin or move on the basic constitutional position; hence the private grinding of teeth and near-despair in government circles at Trimble's success. They are less open in that respect than Ken Maginnis or some of the fringe Unionist parties. But within that rigid framework, Trimble is a much more active and flexible thinker than old Jim Molyneaux was.
He wants, above all, to be a politician who does things. He's despaired at the way legislation for Ulster is rammed through by ministerial Orders in Council and he wants an assembly with real powers over daily life in the province. He speaks about helping the nationalist community with a Bill of Rights and European-style agreements on the treatment of minorities. He is trying to disentangle his party organisationally (though not emotionally) from the Orange Order. He portrays himself as a reformer, in short, on everything except the really big stuff.
This is, of course, far short of what the nationalists say is their bottom line. It may yet help to return Ulster to the cycle of violence and despair. But it suggests a style of Unionism that will be harder to sideline; a Unionism with a voice and agenda of its own.
It also helps to demolish the previous London strategy of dividing Unionism into acceptable and unacceptable parties. The Whitehall mantra has been that ''nothing is agreed until everything is agreed, but not necessarily by everybody''. This implies that a full political deal can be worked out excluding the most hardline Unionists, such as Paisley, and then imposed at a final push.
That strategy will be derailed and probably finished off if Trimble and the DUP start to work more closely together. By holding out an open (red) hand to them, Trimble ends any prospect of divide and rule by London. However distasteful it may be to ministers (and it is, very) they may now have to grapple with Unionist ultras as well as the House-trained UUP. There would then be, as it were, a pan-Unionist front as well as a pan-nationalist one.
The question for the governments and the nationalists is whether Trimble, as the dominant figure in that front, has the imagination and courage to reach out and make a deal which involves referendums and at least some of the cross-border dealing he instinctively recoils from.
In principle, as the conservative, recently elected new leader of the UUP, he is in a strong position to move if he wants to. Some of the comparisons being made with De Klerk's opening to the ANC, or Richard Nixon making peace with Communist China, may be far-fetched. But at least David Trimble won't have to be looking over his shoulder all the time trying to work out what David Trimble thinks.
But will he? The answer to this is buried deep in Trimble's soul. He is a curious mixture of deep, radical Unionist and modern politician. He will march at the head of an Orange procession, defiant grin in place, with all the romantic and anti-Catholic passion of old Unionism striding in step behind him. I think he has quite a dark imagination. He has also lost his temper on several occasions; one minister talks of the ''Ulster flashes'' of scarlet that show on his cheeks when he's angry.
Yet at Westminster he will talk with restrained and precise eloquence about the minutiae of European law and parliamentary arcana, sounding like a more modern, liberal politician than many Tory or Labour colleagues.
He is something rather new, a modernising but utterly committed Ulster Unionist. To bien-pensant opinion that probably sounds about as likely as finding a vegetarian headhunter, or a druid with a PhD; but it is real and fascinating and of great importance. Trimble could yet go either way. He could become the grand old man of intransigent Unionism as the province returned to cycles of violence and hatred. Or he could be the breakthrough politician who leads Ulster into a new era. If the IRA finds a way through the decommissioning row, the spotlight will be quickly upon him.
Old Adam or better nature? I think he will be difficult, and sharp, and unfamiliar, and it is clear that these are exceptionally dangerous and sensitive times. But it seems a little odd to go on for years about stupid Unionists and then panic when you get a clever one. And people change - that's part of the lesson of the past 12 months. This man has a conscience and a fast mind. And for the time being, he is the future of Northern Ireland.