A week ago the Democratic primary race was over. This week, it’s back on again.

Where have we heard this before? The answer is: after almost every big primary day since the voting started back in January. The latest result on Tuesday – a massive, 35-point plus victory for Hillary Clinton over Barack Obama in West Virginia will doubtless revive the idea that the race is still on, and that she might, just might, still have a shot.

There’s an inevitable tendency in the media, as this remarkable primary campaign refuses to die, to portray it as a narrative of ebb and flow; of political events that shift the voters’ attitudes towards the two candidates.

When Mrs Clinton wins a primary it’s because she’s fought back hard, discovered her voice, or because Mr Obama has run into trouble over Rev Jeremiah Wright or something condescending he’s said about working class voters. When he wins, it’s because he’s put those troubles behind him, or Mrs Clinton has committed some terrible gaffe about dodging sniper bullets in Bosnia.

But the reality is rather more prosaic; the contest is unfolding in a much more static and predictable way than that frame of analysis suggests. The race only appears to change each week with different results in different states, but in reality, the outcome in each of these states is heavily dependent on the demographic makeup of that state.

The two candidates are so locked into their demographic bases of support, that , if you had looked forward two months ago to the West Virginia primary on Tuesday you could have predicted the outcome to within a few percentage points. In fact, many smart political pundits steeped in the minutiae of state demographics, did just that.

In fact there’s a sense in which the Democratic primary long ago ceased to be an election turning on political decisions and became instead a kind of census.

Since the Super Tuesday primaries three months ago a clear pattern has held, whatever the events that have dominated the news. If you’re white, working class, older, less well-educated, poorer, female, or Hispanic you’re going to choose Hillary Clinton. If you’re black, or younger, better educated, more affluent white, you’re with Mr Obama.

So in states where white working class voters tend to dominate – Ohio, and Pennsylvania, for example – Mrs Clinton won with solid majorities. In states with large black votes, Mississippi, North Carolina, or in states with younger, more affluent voters, such as Virginia, Mr Obama has won.

West Virginia was right in the heart of Clinton country. It is Appalachia; a bastion of less affluent, white and older voters. The neighbouring counties of other Appalachian states – western Pennsylvania, eastern Ohio, and eastern Tennessee – were some of her strongest regions in the whole country.

Next week, Kentucky – another state with a strong Appalachian flavour – will vote and it will be astonishing if Mrs Clinton doesn’t win by another huge margin – whatever political news actually happens in the next six days.

So what does this tell us about the eventual outcome? Barack Obama is still the prohibitive favourite because his collation is just a bit larger than Mrs Clinton’s. Her only hope is to rack up massive popular vote totals in Kentucky and on June 1 in Puerto Rico.

If her margins of victory there are bigger by a substantial margin than Mr Obama’s expected wins in Oregon, Montana and South Dakota, she still might, on some measures just get accumulate more popular votes than Mr Obama overall. She will then try to persuade the critical superdelegates that she has a real claim on the nomination.

But it’s a very, very long shot. The superdelegates are already streaming into Mr Obama’s camp and only some sort of shock will stop them from giving him the majority he needs quite soon.

The bigger question is what does all this demography mean for the general election – Mr Obama v Republican John McCain in November?

That’s harder to gauge. The Clinton team insist that Mr Obama’s weakness among white working class voters will be an Achilles heel in November.

But many of those voters – despite opinion polls in West Virginia on Tuesday showing a majority of Mrs Clinton’s voters might not vote for Mr Obama in November – will still vote for the Democratic candidate, given the way political circumstances favour the Democrats.

But at this stage we cannot know how much of this remarkably stable demographic pattern will carry over to the general election. What we can say with some confidence is that Mrs Clinton’s supporters – and their ambivalence towards Mr Obama – remain Mr McCain’s best hope to pull out a win against the odds in November.

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