An internal revolt within Germany’s Social Democrats is threatening the whole process of forming a new government in Berlin. The powerful head of the SPD Franz Muentefering has said he is stepping down after party leaders voted against his candidate for the post of SPD general secretary.The move plunges the party into crisis in the midst of talks on forming a government with Angela Merkel’s conservatives. Muentefering had been expected to wield ample power in a new cabinet in the dual roles of labour minister and vice chancellor – posts he may now decline to take up. Should Muentefering pull out of the new government, it could have far-reaching consequences, prompting a breakdown of talks and new elections if the conservatives feel they can no longer negotiate with the SPD. Leader of the Christian Democrats’ partners, the CSU’s Edmund Stoiber, saysMuentefering is a “cornerstone” of any coalition, and has left it open whether he would join the government. The SPD holds its party congress in two weeks’ time, where it will decide whether to approve a coalition agreement with the conservatives and set the stage for the first coalition of the two top parties since the 1960s.