In the only official policy position ever taken by the American Political Science Association, it advocated the transformation of American political parties into a strong, centralized two-party system. Olson has proposed a detailed explanation of why Westminster political systems and parties will produce more efficient public policy than weak, decentralized political parties. He argues that centralized political parties in two-party political systems are ‘encompassing’ and, hence, have an incentive to minimize redistributive policies. Olson thus provides a justification for the policy position taken by the APSA. I evaluate Olson's explanation from the perspective of Tullock's rent-seeking behaviour argument and the deadweight losses needed for Olson's argument to hold. An alternative formulation of encompassing organizations is presented and contrasted with Olson's definition as it applies to political institutions. Finally, an empirical test of the responsible and Westminster party systems arguments is provided. The evidence presented here rejects the claims of the Westminster and responsible party models.