It is only a by-election. And the seat may not even change hands. The Liberal Democrats should hold Eastleigh on Thursday. Although the temptation has been to see it as a great moment in the coalition story, or even the Labour story, it will make about as much difference to British politics as that meteor strike in Russia.
Unless Ukip wins it, in which case it may destabilise the Conservative Party beyond repair. But if the Lib Dems hold Eastleigh, it will merely confirm things that we ought to know already, such as that the Lib Dems are resilient. Although nationally they have lost more than half of the 24 per cent of people who voted for them last time, their activists are in good shape. They are not as demoralised as Labour or Conservative supporters assume that they must be. They believe in coalition and compromise, as a matter of principle. For many of them, the vilification of Nick Clegg over the broken promise on tuition fees is a badge of their coming of age as a party.
They were expecting government to be tough. Chris Huhne, Eastleigh's former MP, said that he expected the Lib Dems to go down to 6 per cent in the polls. They haven't quite, though they have hit 7 per cent several times. But they still have councillors, especially in places such as Eastleigh, that give them a local machine. At the next election, they will be good at holding their seats. They won't be able to pose as the purists of powerlessness, but Eastleigh reminds us what shape-shifters they can still be. In 2015, voters who don't like David Cameron but can't bring themselves to go for Ed Miliband might still make Clegg the "none of the above" option.
Although Lib Dems believe in coalition, in Eastleigh they have been completely ruthless in pretending that this coalition is nothing to do with them. Watching the former Lib Dem leader on the BBC's Question Time recently, a friend said: "When Menzies Campbell finds out who is responsible for propping up this dreadful government, there'll be trouble." In by-elections, people usually look for the most effective way to vote against the Government, and in Eastleigh, somehow, the Lib Dems have managed to be the protest vote against a Tory-led government of which they are part.
So, yes, it is a mark of Labour's failure that the anti-government vote in Eastleigh is a choice between the Lib Dems and Ukip. Even Tony Blair would have struggled to make Labour the natural party of opposition in that part of Hampshire, but if John O'Farrell, Labour's candidate, comes fourth on Thursday, it will make the rebranding of the party as "One Nation Labour" look a bit thin. It is the right idea, but everyone knows that it cuts against the instinct of the leader and his Shadow Chancellor, which is to draw dividing lines where ever possible.
Thursday's result will also confirm that the Conservative Party has a serious leadership problem. Its leadership is not the problem, but the party is, in that it does not want to be led. When Maria Hutchings comes a poor second - or third - Tory MPs will show their familiar restraint and discipline by blaming the Prime Minister, Nick Clegg, the coalition, the EU, meteors in Russia and George Osborne's refusal to accept that cutting tax rates raises revenue, which means he should cut all taxes to zero.
Those Tory MPs, whose numbers seem to be growing, who think that they failed to win a majority at the last election because the party wasn't right-wing enough will view defeat in Eastleigh as proof that they should move to the right. Never mind that Hutchings is an anti-EU, anti-abortion, speak-as-she-finds right-winger.
Such PUP (parallel-universe politics) will make life difficult for Cameron and Osborne in next month's Budget, in which they want to do boringly sensible, centrist things. Tory disunity is more of a problem for the Chancellor than, for example, Labour's response to the UK's loss of its Aaa credit rating. Moody's downgraded us because Osborne is making less progress in cutting borrowing than expected. Ed Balls says we should borrow more and that credit ratings agencies don't matter. His claim that Osborne has been "humiliated" is true enough, therefore, but less than wounding.
Most by-elections don't matter much. Even Bermondsey, 30 years ago today, though it was a marker of Labour's nadir, was offset by Labour's holding on in Darlington a month later. The one thing that would kick things off in Eastleigh, though, would be if Diane James, the Ukip candidate, were to win.
It should not matter if a pure protest party, the policies of which make no sense whatever, wins one freak by-election, just as it did not really matter that George Galloway won Bradford (he thought it was Blackburn) West. But it would drive the Tories over the brink.
I don't think the Conservatives could have won Eastleigh. By-elections are for kicking the Government. But Ukip is a kind of right-wing Tory party for an alternate universe; if it won it would break the Tory space-time continuum. Whoever they lose to, the Conservatives' reaction to defeat will make it harder for them to win the next general election.