At least since Madison railed about the mischiefs of faction, critics of U.S. political institutions have worried about the influence of organized interests in national policymaking. In this century, one of the most eloquent critics of the interest group system was E. E. Schattschneider, who warned of the inequalities between private, organized, and upper-class groups on the one hand and public, unorganized, and lower-class groups on the other. The pressure system, he argued, “mobilized bias” in national policy-making in favor of the former, against the interests of the latter, and hence against the interests of U.S. democracy. Such concerns have hardly abated thirty years since the publication of Schattschneider's essay. In particular, the precipitous growth in the number and financial strength of political action committees has refueled the charge that moneyed interests dominate the policy making process.

Despite the claims of the institutional critics and the growing public concern over PACs during the last decade, the scientific evidence that political money matters in legislative decision making is surprisingly weak.