How do marginal voters differ from regular voters? This article develops a method for comparing the partisan preferences of regular voters to those marginal voters whose turnout decisions are influenced by exogenous factors and applies it to two sources of variation in turnout in the United States—weather and election timing. In both cases, marginal voters are over 20 percentage points more supportive of the Democratic Party than regular voters—a significant divide. The findings suggest that the expansion or contraction of the electorate can have important consequences. Moreover, the findings suggest that election results do not always reflect the preferences of the citizenry, because the marginal citizens who may stay home have systematically different preferences than those who participate. Finally, the methods developed in the article may enable future researchers to compare regular and marginal voters on many different dimensions and in many different electoral settings.