The same year in which Sinclair's book was published, Sarah Binder and Steven Smith gave us the definitive reappraisal of that most distinctive of all Senate institutions, the filibuster, and tracked its evolution from a seldom-used device to a phenomenon so commonplace that majority leaders routinely file cloture petitions with any bill with even the mildest scent of controversy. The year 1999 saw the publication of Frances E. Lee and Bruce I. Oppenheimer's Sizing Up the Senate a study imaginative in conception and skillful in execution that examined the effect of constituency size on the behavior of senators. One might have assumed that somehow senators from sparsely populated Western states and densely peopled Eastern states were different, but Lee and Oppenheimer persuasively codified that hunch with empirical rigor.

In that tradition of studies that focus on what makes the Senate distinct, we now have Wendy J. Schiller's Partners and Rivals: Representation in U.S. Senate Delegations. Schiller combines gold-standard methods with a perceptive eye to examine the complex relationships that exist between senators who represent the same state.

The author astutely conceives of her study as an examination of a two-member constituency, thereby assuming that one senator's actions will, in some way, have an impact on the other. Those who might imagine that U.S. senators are so sovereign and individualistic that they have only the most glancing relationship to their same-state colleague are in for a surprise, because even when the two senators cannot even abide each other, their actions are profoundly affected by the existence of what amounts to a conjoined constitutional twin. It is the very indistinguishability of the two same-state senators in terms of their formal powers and the congruent boundaries of their constituencies that prompts the electoral imperative that they try to differentiate themselves. It is this elaborate and purposeful process that Wendy Schiller describes and analyzes so effectively.

Understanding why this desire to differentiate is so critical for senators, the author begins with the simple but essential observation that every state has a senior senator and a junior senator. Somebody has gotten there first, and the latecomer must, in some politically useful manner, adapt to that fact. If the two senators happen to be of the same party, the problem for the junior partner is compounded because even if the later-arriving senator coveted the same committee assignments as the senior colleague, Senate rules generally forbid two members from the same state and party from service on the same committee. This institutional rule, while problematic on its face for the junior senator, actually contributes materially to the quest for differentiation.

Schiller's inquest into the dynamics of same-state senator relationships delves into such essential areas as bill cosponsorship and the extent to which the two collaborate on legislation, and it discovers, not surprisingly given her overall theme of the imperative of differentiation, that their bills and amendments rarely overlap. There are, of course, areas of legislative action in which efforts at differentiation would be counterproductive, especially for senators from the same state, and that is roll-call voting. Indeed, especially on issues affecting their jointly held constituency, there is notable convergence, but Schiller is emphatic in pointing out the limitations of reliance on roll-call voting data for purposes of gauging differentiation and for evaluating the quality of the representation that senators provide. She echoes Richard Hall's observation in Participation in Congress (1996) that studies that focus on the activity on which legislators spend the least amount of time (casting recorded floor votes) presents us with an incomplete picture of the legislative process.

Schiller's writ runs more broadly than producing findings on the maneuvering of senators to attain the maximum degree of perceived separation from their same-state colleagues. She provides, in her final chapter, some broad observations on the quality of dual representation and concludes that senators pursuing their impulse to differentiate themselves in the minds of voters provide a better and more complete form of representation than if both were focused on the same narrowly drawn list of interests and public constituencies.

Rather than cancel each other out, same state senators from opposite parties tap into vastly different sources of support, champion diverse causes, and draw resources from distinctive collections of contributors. Whatever the partisan configuration of a state's Senate delegation, the very fact that there is one senator looking over the shoulders of another senator is a fairly effective check against senatorial sloth. If dual representation did nothing else, it would keep both parties on their toes.

In her use of a variety of methodologies and by interweaving those findings derived from statistical operations with interview materials, Wendy Schiller has produced a book that is satisfying substantively and also a pleasure to read. Given what she set out to do, she has accomplished it in grand style. I doubt that there are many in our profession who could have done it better.