The same pattern, albeit at a higher plane thanks to the IRA’s ceasefires and the peace process, is detectable since 1998. In that year’s Assembly election, Sinn Fein won 142,858 votes; it peaked three years later with the election of four SF MP’s in the 2001 Westminster poll at 175,392 votes but has declined in the subsequent two elections, the last of which saw Bairbre de Brun win a seat to Strasbourg but Sinn Fein’s vote fall to 144,541. The image in the media is of a Sinn Fein vote that arches ever upwards; the reality is more complicated.

Hand in hand with this has been a steady but relentless decline in the SDLP vote. In 1998 the SDLP won 177,963 votes and was comfortably ahead of SF. Last week the party, minus John Hume, slumped to 87,559, nearly 57,000 votes behind Sinn Fein.

The temptation, to which so many reporters succumb, is to present this as being somewhow about militant Republicanism supplanting constitutional Nationalism. To be sure there is no doubt that Sinn Fein’s growth has come in large part from the SDLP’s decline but since there are now next to no ideological distinctions between the two parties this is a phenomenon with little political significance; the important differentiating factors these days are more to do with age, energy, style, marketing and money than attitudes towards the British presence and the Unionists. It is as if Tweeledum was to steal Tweedledee’s lollipop; would anyone care or even notice?

A much clearer and revealing explanation of Sinn Fein and SDLP voting patterns can be got by examining the total Nationalist vote and placing its performance in a recent historical context.

Once that is done it becomes clear that Nationalism's two most impressive performances came in the 1998 Assembly election, when a total of 320,821 Nationalists turned out and in the 2001 Westminster poll when 345,257 voted.

A tentative but credible explanation for these two results goes as follows: Nationalists come out to vote in large numbers when there is a chance of their representatives grabbing a slice of power at Stormont, as in the 1998 poll, or when there is a chance to take seats away from Unionists, as in the 2001 election.

Contrast those two elections with the the 2003 Assembly election, to a set of suspended institutions with little if no prospect of exercising power, when 280,305 Nationalists voted or the 2004 European election when only 232,100 nationalists voted in an election most people believed was in the DUP bag. Between 1998 and 2004 the total Nationalist vote has declined by a third.

The conclusion is inescapable: Nationalists are more likely to vote when there is an opportunity to take a kick at the Unionists, either by taking from them a seat or two or obliging Unionists to accept Nationalists sitting with them around the cabinet table as equals.

So what are the lessons for Sinn Fein in all this? The next big electoral test will come at next year’s Westminster poll but this time round the chance that Sinn Fein can steal seats from Unionists, like they did in Fermanagh-South Tyrone or West Tyrone in 2001, will be minimal. If SF gain this time it will at the expense of the SDLP, in South Down, Foyle and Newry-Armagh. They will probably succeed but there is not much incentive there for the overall Sinn Fein vote to rise; more likely that demoralised SDLP'ers will stay at home.

The best set of circumstances for Sinn Fein’s vote to rise is when Nationalism as a whole sees a chance to exercise power at Stormont. If there is a lesson for Gerry Adams and his advisers in the 2004 election it is to get back into Stormont, even if that means having to satisfy the DUP’s demands to wind up the IRA. Otherwise the decline in the party’s vote will just continue and that will inevitably impact adversely on the party's image as a growing force in the South.

In the 1980's, IRA violence was largely responsible for ending Sinn Fein's then cycle of election successes; if the Provos continue to refuse to decommission the IRA then they run a great risk of the same thing happening again. Far from being an unmitigated triumph for Sinn Fein, it would be more accurate to view the 2004 election as a yellow card from the Nationalist voter.