Political science research comes to different conclusions about which policy dimension primarily drives voting behavior in the United States. Some emphasize economic preferences as central in explaining voting decisions , others stress socio-cultural attitudes. In this paper, we propose a new perspective on the ideological structure of US voter preferences that reconciles these diverging finding. We make the case that the two dimensions are ideologically connected and are, at least partially, functional equivalents. Although voters may have well defined economic and cultural preferences, the two do not work additive in the vote choice mechanism: Voter preferences on the two dimensions are non-separable. We formally derive how non-separability of preferences can originate from one underlying ideological dimension that drives voting behavior. Analyzing survey data on US presidential elections from 1996 to 2012, we estimate to which extent economic and socio-cultural preferences are non-separable. Evidence from an original experiment underlines that non-separability is due to one-dimensional ideological considerations of voters. These findings inform us how voters and candidate campaigns use non-separability as an effective heuristic device to reduce the dimensional complexity of political choice and communication.