The aforementioned missing piece of the canvas is the coalition of voters put together in 1997 by Tony Blair (and Gordon Brown) which managed to turn a winning position against a disliked Tory government into a landslide.
Labour's fear now is that David Cameron (much derided for his adoption of Blairite strategies) is about to do the same to them.
But in Labour's case the consequences might be even worse.
At their lowest ebb the Tories could depend on a solid core vote in the south of England. Indeed they won the most votes in England in 2005, even though Labour still won with a healthy majority thanks to seats in Scotland.
The other factor in Labour's pre-eminence was the fact that anti-government votes went more or less equally to the Tories and the Liberal Democrats, plus a few to the Greens and UKIP.
But in the recent Crewe and Nantwich bye-election the votes went mostly to the Tories (although the Liberal vote actually held up pretty well).
So the story, or narrative as we're supposed to call it these days, isn't just about Gordon Brown and his failings. For most Labour MPs, it's about the danger of a complete wipe-out at the next election, supposedly in 2010.
Few Labour MPs think they can win the next election under any leader. What they want is the chance to keep their seats and remain a big party in the land. At best they hope for a hung Parliament.
The media, of course, are in full hue and cry, hoping for a Brown defenestration to add spice to the summer.
Of Labour's usual allies, The Guardian is after his blood, with Saturday columnist Martin Kettle leading the pack. The Observer is having serious doubts, led by star columnist Andrew Walmsley, and The Independent has pretty well given up on him too. The Mirror is still more or less loyal, but it has nowhere to go but Labour.
One reason why elements of these papers are, in effect, trying to lead MPs by the nose is their disillusion with the way that Brown has followed the Blair practice of pandering to the right-wing press.
Brown was supposed to be different to Blair, and part of this (as far as the liberal papers are concerned) should have been the abandonment of the Daily Mail and The Sun as the unofficial arbiters of government policy.
But Brown has been, if anything, "worse" than Blair. And look where it's got him.
His next big test (arguably the biggest) is the imminent vote on 42 days detention for terrorist suspects, a measure that even Home Secretary Jacqui Smith, responsible for pushing it through, doesn't really want, according to some interesting hints over the weekend.
This could be the catalyst for the fabled delegation of ministers to visit Brown to demand his resignation. If the cabinet don't want it, the backbenchers don't want it, the rest of the house doesn't want it and, in the media, only the Sun supports it, then Brown will be committing hara-kiri.
If Brown has the sense to backtrack, even at this late stage, he may survive and his party might rally to him as they tire of the press baying for his blood.
But knowing Brown, it's a long shot.