When Europe's social democrats staged their first Progressive Governance Conference in 1999, the centre left held power in 13 of the European Union's 15 member states. Since then, the left has lost ground in almost every country. Just eight of the European parties that attended a similar gathering in Oslo between 12 and 13 May are in government.
Amid the gloom, delegates consoled themselves with the thought that Dominique Strauss-Kahn, the presumptive French Socialist Party candidate, would likely defeat Nicolas Sarkozy in next year's presidential election and become the second Socialist leader of the Fifth Republic. But Mr Strauss-Kahn's arrest on suspicion of attempted rape has put paid to such hopes. Whether or not he is found guilty (and he maintains his innocence), both his candidacy and his political career are over.
The downfall of the man France knows as "DSK" is undoubtedly a blow to the French left. As the head of the International Monetary Fund (IMF), he steered that institution, hitherto a bastion of neoliberalism, in a more progressive direction with his support for fiscal stimulus and his emphasis on job creation. Opinion polls consistently showed that he was the candidate with the best chance of denying Mr Sarkozy a second term in the Élysée Palace. But it is symptomatic of the crisis of the French left that many Socialists have already resigned themselves to defeat in 2012. A progressive party should never have allowed itself to become so dependent on one man.
In his recent lecture on the crisis of the European centre left, David Miliband noted: "It is ironic but deeply indicative that it takes a man with the economic credibility of IMF managing director to give the French left its best chance of winning its first presidential election in four." What Mr Miliband meant by this was that the French Socialist Party, like its centre-left counterparts elsewhere, had failed to establish a convincing narrative on the financial crisis and its aftermath. The left's hesitant response to the crash meant that an argument about capitalism became one about debts and deficits.
Labour's poor performance in the recent local and devolved elections means that Ed Miliband's leadership style has come under renewed scrutiny. But this debate should not obscure the wider challenges for the party: to rebuild its membership base, restore its economic credibility and offer
a new social-democratic model that is as appealing to the people in the south of England as it is to those in Scotland and the formerly industrial north. These tasks will not be accomplished by one man alone.
Similarly, although the Scottish National Party's victory was a personal triumph for Alex Salmond, it was his party's progressive and coherent programme - no tuition fees, no NHS prescription charges, free school meals for all five-to-eight-year-olds - that propelled it to an overall majority.
The lesson for the left is that although an effective leader may be a necessary condition for success, it is not a sufficient one. Short-term popularity is no substitute for genuine intellectual renewal. If it is to prevent another decade of centre-right hegemony, the left must face up to this truth.