A nationally representative sample of US adults completed two political categorization tasks. The first was to identify the political parties for hypothetical candidates with information given about demographics and stands on issues. The second task was to decide whether to vote for each candidate. On the identification task, judgments about whether a person is a Democrat were almost a perfect mirror image of judgments of whether a person is a Republican. In general, respondents were very successful in the identification task; there was a strong correlation with objective probabilities. Likewise, respondents were successful at the voting task, in terms of their own party interests. Success at these two tasks was positively correlated with a measure of political knowledge. The pattern of responses was also influenced by the political party of the respondent; suggesting that feature weights depended on party membership. Implications for models of categorization and reasoning are discussed.