In previous chapters, we have seen that both the effects of nonpolicy predispositions of voters and the threat of abstention can motivate policy divergence by candidates. In addition, such divergence may be engendered by the potential entry of third parties, the influence of party activists, or – in America – by the polarizing effects of primary elections, and the degree of divergence may be augmented by voter discounting of party positions.
While the approaches already described have generated substantial study, perhaps the most widely cited motivation for policy divergence is that the competing candidates or party leaders have policy motivations – that is, that politicians seek office in order to implement desired policies, rather than proposing policies in order to win office. As Donald Wittman (1990: 66) has argued, this motivation fits comfortably within the spatial modeling framework, since it is strange to think that voters' decisions are moved by policy concerns (a key spatial modeling assumption) but that politicians do not similarly care about policies, except as a means of winning office. And indeed, empirical studies of elite decision making conclude that politicians at times attach considerable weight to pursuing policy objectives (see Fiorina 1974; Muller and Strom 1999). In this and the following chapters, we investigate the effects of parties' policy preferences on their positioning in two-party contests.
In the years since Wittman's (1973, 1977, 1983) seminal articles, spatial modelers have elaborated many approaches to theorizing about policymotivated politicians' strategic choices (Cox 1984; Calvert 1985; Chappell and Keech 1986; Mitchell 1987; Brams and Merrill 1991; Londregan and Romer 1993; Kollman, Miller, and Page 1992; Groseclose 2001; Roemer 2001).