Pundits and scholars laud online campaigning for its potential to democratize politics and praise the 2008 Barack Obama campaign for using new information technologies to mobilize voters. Underneath these extraordinary forms of technologically-enabled political participation, however, is an infrastructure and industry for political data that has received far less attention. To help fill this gap in scholarly understanding, we provide an overview of the data practices of political campaigns over the last decade and take a particularly close look at many of the new tools used by the Obama campaign. As a call for further research, we then outline a set of potential normative concerns about this use of data. We suggest that the data practices of campaigns and other political organizations may undermine important democratic norms. Campaigns erode privacy and narrow political debate by using data on citizens and social networks to tailor messages and communicate with narrowly-defined segments of voters. The lack of policy oversight erodes institutional transparency and leaves citizens vulnerable to breeches in personal data.