Governing parties face two fundamental tasks: they must pursue policies effectively, and they must win elections. Their national coalitions, therefore, generally include two types of constituencies--those that are important for policy-making and those that make it possible to win elections. In effect, governing parties must bring together a policy coalition and an electoral coalition. This distinction sheds light on how the transitional costs of major economic policy shifts can be made sustainable in electoral terms. It also provides a starting point for analysis of how two of Latin America's most important labor-based parties, the Peronist party in Argentina and the Partido Revolucionario Institucional (PRI) in Mexico, maintained electoral dominance while pursuing free-market reforms that adversely affected key social constituencies. Peronism and the PRI are conceived of as having encompassed historically two distinctive and regionally based subcoalitions: a metropolitan coalition that gave support to the parties' development strategies and a peripheral coalition that carried the burden of generating electoral majorities. This framework permits a reconceptualization of the historic coalitional dynamics of Peronism and the PRI and sheds light on the current process of coalitional change and economic reform.