The character of the U.S. Senate has changed markedly over the last 30 years. The Senate can no longer be characterized as a well-bounded entity ruled by an “inner club” of insular grandees. Increasingly, rather, the Senate is a great forum, an echo chamber, a theater, where dramas—comedies and tragedies, soap operas and horse operas—are staged to enhance the careers of its members and to influence public policy by means of debate and public investigation.

Its special role today in the contemporary American political system is as an incubator of policy ideas and political innovations (Polsby 1984). This stands in dramatic contrast with the Senate as late as the 1950s, which was far more a body that had positioned itself as a critic and a respondent—frequently an inhospitable one—to the political innovations hatched in the executive branch and by activist presidents and forwarded to it by the House of Representatives. Thus over the last three decades the Senate has evolved from a rather negative repository of states-rights thinking, dominated by a mostly southern-led “inner club,” and hence an explicit agent of the devolved aspect of the federal system, into a predominantly nationally-oriented body.

The principal agent of this transformation has been the very great change in the life chances and therefore in the political ambitions of a large number of U.S. senators. Earlier, not so many of them entertained presidential ambitions. Today, the Senate is the main institutional source of presidential hopefuls, and for a large fraction of senators such hopes play a significant part in guiding their behavior in the Senate.