In the context of a national election, this study explores more than 69,000 Twitter messages containing mentions of political parties and about 2,500 related user profiles to investigate the network structure of political microbloggers with respect to, first, their party preference and, second, the topics they discuss. We find that political microbloggers tend to follow like-minded peers. Microbloggers in a cohesive group tend to have the same political preferences. In addition, we conduct a content analysis of the political debate on Twitter to explore which topics and politicians are discussed and whether this debate reflects an ideological divide among participating users. While there are some discussion topics that are dominated by politically like-minded microbloggers, the majority of topics is discussed by a diverse group of microbloggers with various political preferences.