How do marginal voters differ from regular voters? This article develops amethod for comparing the partisan preferences of regular voters to thosemarginal voters whose turnout decisions are influenced by exogenous factorsand applies it to two sources of variation in turnout in the UnitedStates—weather and election timing. In both cases, marginal voters are over20 percentage points more supportive of the Democratic Party than regularvoters—a significant divide. The findings suggest that the expansion orcontraction of the electorate can have important consequences. Moreover, thefindings suggest that election results do not always reflect the preferencesof the citizenry, because the marginal citizens who may stay home havesystematically different preferences than those who participate. Finally,the methods developed in the article may enable future researchers tocompare regular and marginal voters on many different dimensions and in manydifferent electoral settings.