NICOLAS SARKOZY ought to be invincible. The president dominates France’s government, over which his prime minister, François Fillon, sits as a figurehead. He has no credible rivals on the centre-right. He has emasculated the Socialist opposition by co-opting its talent. Though France has suffered in the recession, with one in ten out of work, he can boast that it has so far fared better than any other big west European economy.

Yet on March 21st voters gave Mr Sarkozy a bloody nose. Regional elections count for little in France and turnout was low. But the 54% share of the vote won by the Socialists (and their green allies) was their best result in 30 years. Mr Sarkozy’s UMP party took only 35% and just one of the 22 mainland regions (see article). The far-right National Front, which Mr Sarkozy defanged in 2007, rebounded to double figures.

Two points emerge from this. The first is that Mr Sarkozy is, for the first time, under attack from his own side. Some say he has been doing too much at once, pushing unpopular reforms too quickly, and not doing enough to keep grumpy voters happy. His limited government reshuffle this week, keeping Mr Fillon in place, suggests that Mr Sarkozy plans to press ahead with his priority of pension reform, notably to raise the retirement age from 60. But his electoral setback will encourage siren voices in the UMP that call for a slowdown in reform.

Mr Sarkozy should press ahead. He was elected in 2007 because he persuaded voters that France needed big reforms. The recession has only strengthened his case. In the euro area, economies deprived of the safety valve of devaluation must make structural reforms to adjust. Most voters have turned against Mr Sarkozy because he has not brought results—and that is largely because he did not stick to his programme.

Hence the importance of the second point: that the Socialists are back from the dead. It would be a mistake to read too much into one result. The Socialists did almost as well in the 2004 regional elections, only to lose the presidential poll three years later. The party lacks a strong challenger to Mr Sarkozy in 2012. But with a majority of voters saying they do not want Mr Sarkozy to run again, the Socialists are newly confident. The party leader, Martine Aubry, has gained stature, so much so that she may fancy her own chances in two years’ time.

Send for DSK

Mr Sarkozy can no doubt bank, as ever, on help from party splits and personal rivalries. Ségolène Royal, whom he defeated in 2007, is eager to run again, as is Laurent Fabius, a former prime minister. But there is one person who polls suggest has easily the best chance of beating Mr Sarkozy in 2012: Dominique Strauss-Kahn, managing director of the IMF. Mr Sarkozy is clearly worried. Insiders say this is one reason why he has opposed a bigger role for the IMF in rescue plans for Greece.

From an independent viewpoint, Mr Strauss-Kahn’s candidacy would be good for the country. Because Mr Sarkozy has upstaged everybody else in French politics in the past three years, he has been tested by remarkably little informed criticism. Indeed, this helps to explain why his record has been disappointing. A proper debate against a credible rival would allow the French to decide if Mr Sarkozy, once a shoo-in for re-election, should instead be only the second president in the Fifth Republic to be voted out after a single term.