The electorate in Britain may be facing what a commentator has called "one of the more crucial elections, a choice between two utterly different futures". Northern Ireland is probably heading for a watershed.
Since the days of electoral sameness, when every Westminster parliament received 12 out of 12 unionists and Stormont elections were a foregone conclusion, there have been many changes and voters have had an extraordinary number of outings. A few stand out. This could be one of them, the results illustrating the disposition of political strength for a decade ahead.
The body politic needs time to absorb major developments. It was hard enough for many when John Hume's last electoral outing saw his party slip behind, and Sinn Féin transcended its origins as mouthpiece for the IRA to become the prime mover in nationalism. There was a further jolt in the 2003 assembly election, when, after a lifetime of glorying in being the outsider, Ian Paisley completed a journey from pantomime demon, as one history puts it, to acclamation as leader of unionism and head of the largest party.
Then last December the DUP briefly looked ready to share power with republicans. There were no maps for this terrain. The concept of Ian Paisley as First Minister in Stormont, Martin McGuinness Deputy First, took time to sink in as a real possibility, and by then the amazing prospect had dematerialised again.
So it was possible to ward off the realisation that any arrangement between the DUP and Sinn Féin would set the DUP up as provider of First Ministers for the foreseeable future, with Sinn Féin in an equally impregnable position.
Only so much shock to the system can be tolerated. When the Northern Bank robbery froze the last likelihood of early progress, it was the perfect excuse to put DUP and Sinn Féin dominance of the new order out of mind.
But May 5th looks set to make ears ring all over again. All the signs suggest that it will confirm the collapse of the Ulster Unionists and the SDLP, leaving politics effectively as a contest between two parties. This poll is likely to appear as striking in retrospect as only a few elections of the past.
There was the "crossroads" election of February 1969, when Ulster Unionist prime minister Terence O'Neill launched his campaign by looking mournfully into the television cameras, intoning: "What kind of Ulster do you want?" in his curious drawl. It was the North's first TV election address, made with no flair.
Pushed hard from London by Harold Wilson's government to make real change, harassed by hardline internal critics of his tentative reformism, and with the young Paisley loud among those who saw the civil rights movement as no more than the IRA in disguise, the election was O'Neill's last throw.
Northern Ireland was at a crossroads, he said, and must choose between progress or disaster.
But the divisions in unionism were exposed, not healed by the election: it would never be a monolith again. Inside two months O'Neill had resigned.
Eight years later the results of the 1977 local government election shook out several unionist splinters, revealing the four parties that would lead the field until Sinn Féin's rise: Ulster Unionists, SDLP, Alliance and DUP, their shares of the vote descending in that order. And there was a major breach in the pattern which had held since the formation of the state. From then on hardly a council was ever controlled by a single party.
The first election for the European Parliament in 1979 was to fill three seats, the third specifically allocated to give nationalists representation.
But John Hume, then deputy SDLP leader, careered in ahead of the two Ulster Unionists, and Ian Paisley had his first validation as voice of unionism with a poll-topping victory in the first count. It was the first proof of the Paisley appeal to an electorate wider than those who supported his party.
The 1982 election to a Stormont assembly marked the arrival as a political force of Sinn Féin, or Provisional Sinn Féin as style had it, with a haul of more than 10 per cent of the vote and five of the 78 seats. Moderate nationalism's answer to the republican challenge was the crafting of the Anglo-Irish Agreement of 1985, meant to assuage nationalist "alienation".
The stage was set for the eventual emergence of the 1990s' peace process.
David Trimble and Mark Durkan know they face redundancy if they fail to top the polls in Upper Bann and Foyle. If either succeeds but their parties continue to slide, the future is little different.
Political life beyond the watershed will be dominated by forces which came into being to wreck the old order. But they are in transit themselves, to uncertain destinations.