If any one constituency is capable of illustrating the "realignment" of unionism, it's Lagan Valley.
Jeffrey Donaldson won this seat, created in 1983, for the Ulster Unionists with a thumping majority in 2001. He reinforced the Ulster Unionist grip on it again in November 2003 Assembly election only to defect to the DUP six weeks later, claiming that he was true to the fundamentals of traditional unionism and that David Trimble had lost his way.
His task this time is to underpin his standing as a DUP member of parliament, to shed any image that he is a defector, and to prove that unionists everywhere are shifting towards the DUP and its push for a "Fair Deal".
Election statistics are firmly in Donaldson's favour. Last time he pulled in 25,966 votes. His share of the vote at 56.6 per cent was the best result for his former party in Northern Ireland.
Séamus Close of Alliance polled a healthy 7,624 - the best result for his party - and he is standing again, confident that his lengthy record in the constituency will stand to him.
Like the SDLP, Alliance is running more local government candidates with a view to boosting its numbers on the council. The DUP then came a distant third with 6,164.
The SDLP and Sinn Féin polled 7.5 per cent and 5.9 per cent respectively.
The question now is can Donaldson take those votes with him and prove to his UUP opponents that he, and not Trimble, is closer to unionist opinion at grass roots level.
Fighting Donaldson is Ulster Unionist newcomer Basil McCrea, a 45-year-old businessman who denies Donaldson's significant vote last time is a personal one.
"Jeffrey is under huge pressure," he says. "Every third door he goes to he gets questioned about jumping ship, that's what people want to talk to him about. They don't like it."
Asked if this means that the DUP man still enjoys two-thirds of popular unionist opinion, he answers: "Some may still like him, but for every Jeffrey fan there's another who simply cannot have him at all."
"If it were a case of Jeffrey having a crisis of conscience about the UUP, then resigning and seeking re-election with another party - that's fine." he claims.
"But unionists here just don't like what he did. You can't run for the UUP then a few weeks later pop up as a DUP man." The talkative Ulster Unionist who beat his party leader's wife, Daphne Trimble, for the nomination, claims the battle on the Lagan Valley hustings has been a "very positive experience so far.
"I'm convinced this battle is balanced 50:50. But the momentum is clearly with us. Jeffrey is making a 'big ask'. Lagan Valley is going to stay with the Ulster Unionists."
McCrea joins the battle with no electoral track record. It's to his advantage, he insists, and he details his business record and his acumen which, he says, makes him well suited to politics.
For his part, Donaldson speaks with more certainty. As he prepares to canvass in the residential area where Trimble lives he is quietly, yet utterly confident that he will be returned to Westminster.
"Traditional unionism is coalescing around the DUP," he says. "I've had people telling me they are Ulster Unionist supporters all their lives, but at the same time they tell me they have always voted for me and will be voting for me in this election."
These people are not abandoning their principles or their outlook, he says, it is the Ulster Unionist Party that has abandoned them.
"For years grass-roots unionists have been disillusioned with the splits within unionism. Like me they want to see a coming together, but David Trimble has made that impossible with his approach."
He believes there won't be an improvement in the unionist mood until Trimble goes.
"In the meantime, people are voting with their feet," he says and abandoning their traditional home.
The DUP has given unionists new confidence, he says, and for the first time unionism has left the negotiating table stronger rather than weaker.
Patricia Lewsley, the SDLP Assembly member and Westminster candidate, testifies to the Donaldson appeal to unionists in the area.
She commends his work rate and his ability to retain a core personal vote. "Even if he takes just 10,000 Ulster Unionists out of 25,000, then he is home and dry with DUP backing. It's likely, but it's not guaranteed," she says.
For her, this election is a push to keep ahead of Sinn Féin and to keep an eye on the next Assembly election - if there ever is one.