On 10 June 2005, the leaderships of WASG and the PDS agreed to form an electoral alliance for the then-upcoming federal elections in September 2005. According to the agreement, the parties would not compete against one another in any district, and followed a joint electoral manifesto. This was intended to benefit both parties, because the WASG is based primarily in western Germany, while the PDS, which was the legal successor to the East German Socialist Unity Party (SED), is strongest in the East. Lafontaine, the former chairman of the SPD, was the WASG's lead candidate.