For over a half century, Anthony Downs'¬"s spatial model of ideologically structured party competition, articulated in An Economic Theory of Democracy, has been deeply embedded in the logic of American political science. An explicit assumption of this theory is that in a system of two-party competition, centrist politics would emerge as parties compete for the so-called median voter. But the highly polarized American politics in the early 21stcentury challenges the broad logic of Downsian two-party democracy. In fact, Downs made no attempt to apply his thinking to the specific context of an American-style two-party democracy characterized by separation of powers, federalism, and a bicameral Congress. In this groundbreaking new work, Lawrence Dodd reassesses the ways in which Downs'¬"s ideas apply to the American context. He draws on Downs'¬"s core argument about ideology-based party competition to develop a theory of cyclical swings between polarized and depolarized party system politics. With these cyclical swings in party system polarization come swings between a more centralized party government structure in Congress and a decentralized committee government structure. The first is focused on the pursuit of new purposes and programs for government; the second is focused on overseeing and enhancing the core functions and existing programs of government. These swings in party system polarization, organizational governance, and policymaking orientation enable Congress to contribute in critical ways to the nation'¬"s capacity to adapt effectively to societal change. Dodd'¬"s arguments about the fundamental relationship between voters, government, and policy outputs represents a new paradigm for the study of American politics in general and Congress in particular.