"This is like a thunderbolt," said Lionel Jospin, a former Socialist prime minister who is close to Mr. Strauss-Kahn, the former head of the International Monetary Fund who was once regarded as the likely Socialist Party candidate to challenge President Nicolas Sarkozy in next year's elections.
Those ambitions came to an end when he was accused of sexually assaulting a housekeeper in a New York hotel in May. The allegations seemed to draw an abrupt and indelible line across his career, forcing his resignation from the I.M.F. as the fissured Socialists began seeking a new presidential champion. But the calculations changed radically after Mr. Strauss-Kahn was released from house arrest in New York on Friday, following accounts by two well-placed law enforcement officials in New York that the case against Mr. Strauss-Kahn was on the verge of collapse due to major questions about the credibility of his accuser.