A theory of income taxation where politicians focus upon core and swing voters

We construct an equilibrium model of party competition, in which parties are especially concerned with their core and swing voters, concerns which political scientists have focused upon in their attempts to understand party behavior in general elections. Parties compete on an inifinite-dimensional space of possible income-tax policies. A policy is a function that maps pre-fisc income into post-fisc income. Only a fraction of each voter type will vote for each party, perhaps because of issues not modeled here or voter misperceptions of policies. Each party’s policy makers comprise two factions, one concerned with maximizing the welfare of its constituency, or its core, and the other with winning over swing voters. An equilibrium is a pair of parties (endogenously determined), and a pair of policies, one for each party, in which no deviation to another policy will be assented to both its core and swing factions. We characterize the equilibria: they have the property that both parties propose identical treatment of a possibly large interval of middle-income voters, while the “left” party gives more to the poor and the “right” party more to the rich. An empirical section uses the data of Piketty and Saez on taxation in the US to assess the model’s predictions. We argue that the model is roughly confirmed.