David McKittrick: There may soon be only one Unionist party

Paisley's party will probably be the only Unionist show in town, with devolution dependent on its assent

Jeffrey Donaldson's resignation from the Ulster Unionist Party could signal a vital fundamental political realignment, since it may cement the Rev Ian Paisley's Democratic Unionists as rulers of the Protestant roost. If, as looks likely, Donaldson and two supporters join the DUP, Paisley will have a strong majority in the Belfast Assembly, holding 33 seats compared to David Trimble's 24. The power balance within Unionism is shifting.

The Donaldson move leaves it next to impossible to see how Trimble can stage a dramatic comeback to restore his party to its traditional place at the head of Unionism. Most are reluctant to write off Trimble, since he has been so central to the peace process and since so much political capital has been invested in him by so many. But his party's prospects are bleak.

The DUP is ahead of him in terms of votes and Assembly members, and is about to overtake him in terms of Westminster seats. Donaldson may have been relentlessly rebellious, but he was also a big vote-getter. Tributes have been paid to Trimble's courage in keeping the Good Friday Agreement going, but a politician needs more than just nerve. He has a poor electoral record, his party sagging at the polls in almost every contest since he became leader.

Its campaign for last month's Assembly elections was a bit of a shambles, one party poster featuring fish and chips to show how British it was. The DUP ran a better-planned campaign, keeping Paisley himself in the background and conveying a sense of efficiency and teamwork.

If as expected Donaldson now joins that team, he will strengthen it, and strengthen too the sense that the DUP is successfully reinventing itself and broadening its appeal from its straightforward kick-the-Pope days. His move is an acceptance that the leadership of the Ulster Unionist Party, which had sometimes seemed within his grasp, is no longer a possibility. It also conveys his belief that the UUP will never again defeat the DUP.

Last month's election is quickly assuming the characteristics of a watershed. On the nationalist side, Sinn Fein overtook the SDLP, and no one can see a way for the SDLP to reverse that. Sinn Fein is at the helm of northern nationalism.

Before the election, Northern Ireland had a four-party structure, with two Unionist and two nationalist parties all within reach of each other. The election changed that landscape with Sinn Fein and the DUP emerging as the big two.

Donaldson's judgement is that the DUP has transformed itself from a Paisley one-man band whose leader used to deride him as "little Jeffrey". Now he hopes it has become a proper political organisation in which he can find a useful home. He is not the first UUP person to join the DUP: other less well-known individuals have already made the leap and become valuable back-room boys for the Paisleyites, helping to give the party new structure and focus. These were early straws in the wind, signalling that energetic younger people were choosing the DUP over the UUP, regarding it as the more dynamic party.

With Donaldson on board the DUP will have, in him, Peter Robinson and Nigel Dodds, three of Unionism's most articulate voices. Trimble, by contrast, has less in the way of political back-up. He will be watching anxiously to see whether more dissidents will now jump ship and clamber aboard the DUP.

The fact that the DUP won the battle within Unionism has meant that recent political activity has concentrated on exploring the party's intentions. The question is whether, having successfully modernised its own structures, it can now take a more modern view of politics. It has certainly significantly softened its rhetoric, speaking of renegotiating the agreement rather than smashing it, leading some to hope it will eventually move to cut a deal.

But since few are confident this will happen, there has been an unavowed Plan B in the background. If the DUP proved unwilling to compromise, then the agenda might have moved back to Trimble, with an attempt to sideline the DUP. This would mean changing the Assembly rules to put him at the head of a new coalition, even though his party would be smaller than the DUP. This idea was surrounded with difficulties, but the new reconfiguration of forces probably means it is no longer a runner.

The DUP, in other words, will probably be the only Unionist show in town, with devolution to be achieved only with its assent. This is galling for many, since although the election delivered a victory for the DUP it also showed a clear overall majority in favour of the agreement. Yet while the advance of the hardliners dismays many, no sense of crisis pervades the peace process. This is principally because of the widespread belief that the extremes are no longer as extreme as they used to be.

Although Donaldson was always more hardline than Trimble, something about his body language conveyed that he was not just a simple hardliner, and would someday be in the market for a deal. He is not moving towards the DUP because he sees it as the party of intransigence, but because he figures it is following the same trajectory as himself.

The next year or so will see an exploration of the DUP position, while Trimble struggles to prevent the disintegration of his party. That party used to be called the Unionist monolith: not any more.