Less than 24 hours to polling in South Antrim, and it's still on a knife edge. The main Ulster Unionist and DUP players know this is a high-stakes contest. The future of David Trimble and the Belfast Agreement could rest on the outcome.
Whether the voters are attuned to its importance could determine the result. David Burnside risked campaigning on a "unity candidate" strategy to win the votes of Yes and No Ulster Unionists. The danger for him is that this tactic could alienate or confuse both pro- and anti-agreement Ulster Unionists.
William McCrea consistently tried to exploit that ambivalent positioning, arguing that voters knew where they stood with him: solidly anti-agreement with no ifs, buts or wherefores.
Mr McCrea will get the DUP vote out. There's no doubt of that. Like Sinn Feiners, DUP supporters are politically astute and concentrated. Many Ulster Unionists inhabit a more nebulous political world. Theirs is not the politics of fundamentalism. Some of them could stay at home tomorrow, figuring this is just a mid-term by-election of no great significance. Others could switch allegiance.
For Mr Burnside's purposes Ulster Unionists must bury their differences on the agreement, and in some cases their antipathy to him, and think party loyalty.
This explains why the UUP has been putting on a show of unity during the campaign, particularly in recent days. The twin brands of Yes and No Ulster Unionism represented by the likes of Lord Molyneaux, Jeffrey Donaldson, John Taylor and David Trimble have stood shoulder to shoulder with Mr Burnside; notwithstanding the fact that some in the pro-agreement camp are antipathetic to their candidate while some in the anti-agreement side don't trust him.
If Mr McCrea wins tomorrow the shock effects will register high on the political Richter scale. Not everyone realises how critical is this election.
Mr Trimble would almost certainly face another leadership challenge; the British and Irish governments would be told bluntly that in the unionist heartland the Belfast Agreement is increasingly unpopular; the SDLP and Sinn Fein would have to consider whether their adamant position on issues such as Patten and flags was antagonising normally moderate unionists from the Good Friday accord.
The DUP deputy leader, Mr Peter Robinson, acts rather coy about Mr McCrea's chances. He affects mock surprise that anyone could expect the DUP candidate to overturn the UUP majority of over 16,000 from the last general election in 1997, realising full well that a better barometer of unionist feeling is the Assembly election of the following year.
In 1998 the UUP polled 13,000 votes, against just under 9,000 for the DUP. That suits Mr Burnside. But when the votes are separated between Yes and No unionists, it becomes clear that anti-agreement unionists won over 15,000 votes, against over 12,000 for pro-agreement unionists. That suits Mr McCrea.
It's obvious therefore that if Mr Burnside is to succeed in his long-standing ambition to enter Westminster, Ulster Unionists must come out in strength and maintain party loyalty.
He and his supporters are also banking on Ulster Unionists, whatever their misgivings, being unable to cross party lines and place their Xs for Mr McCrea.
"If Nigel Dodds were the DUP candidate it would be a different matter, but I don't think Ulster Unionists could vote for Mr McCrea's firebrand form of unionism," said one Ulster Unionist, ruminating on the DUP man's appearance with the murdered LVF leader, Billy Wright.
Mr Trimble knows this election is as much about his future as that of Mr Burnside. The DUP has much to gain. If Mr McCrea doesn't take the seat but comes close, Dr Paisley and Mr Robinson will claim to have overturned a 16,000 majority.
If Mr McCrea wins, the DUP crowing will be heard in UUP, SDLP and Sinn Fein headquarters, and in Dublin and London. Mr Trimble is also conscious that the unionist apathy factor could bring him down. He desperately requires Ulster Unionists to understand the potentially apocalyptic implications if Mr McCrea is victorious.
"I sound a warning to the unionist community," said Mr Trimble with great seriousness yesterday. "Ulster Unionism's biggest enemy in this election, as in other elections, is complacency. There is more at stake in this election than any other in recent times.
"All Ulster Unionists must make their vote count. Those who want to drag unionism back into the dark ages where it has no power and no influence must not be allowed to succeed."