By Ray Furlong
BBC correspondent in Berlin
The leader of the German Social Democrats (SPD), Franz Muentefering, has fuelled doubts about the new ruling coalition by resigning as SPD leader.
Mr Muentefering played a key role in the coalition talks
He said he would not seek re-election to his post next month after losing a key vote within the party.
He is one of the key architects of the bi-partisan coalition government with the conservative Christian Democrats.
His position as employment minister and vice-chancellor in the emerging government is now in doubt too.
Mr Muentefering's decision to quit suggests that the party could be an unstable and difficult coalition partner, riven by internal power struggles between its right and left wing.
1. Christian Democrats/Christian Social Union (CDU/CSU): 226
2. Social Democrats (SPD): 222
3. Free Democrats (FDP): 61
4. Left Party: 54
5. Greens: 51
He made his announcement after losing a vote in the leadership over who would take the number two job in the party.
His favoured candidate was defeated by a leading left-winger - a slap in the face for Mr Muentefering.
Mr Muentefering said he would consider his position in the new coalition government after a special party conference in two weeks' time.
He was once the darling of the SPD rank-and-file. His departure suggests the political price he has had to pay for his support of painful welfare reforms pushed through by the outgoing government over the last few years.