Many public opinion theories suggest that all citizens rely on core beliefs and values to guide their preferences on social and political issues. The "Expertise Interaction" model of public opinion challenges this position by arguing that the ability to use core principles in this manner is a function of political expertise. However, there is very little direct evidence that measures of expertise strengthen the relationship between measures of core beliefs and policy preferences. This article analyzes the effects of expertise on principled political thought across several issues with data from the 1990 and 1992 National Election Study surveys. The results demonstrate that the expertise effect is surprisingly limited. These findings call into question the presumed ascendancy of the expertise interaction model.