Dennis Mueller concisely expressed the concern of many economists about the efficacy of vote trading:
. . . when voters are able to make and keep vote-trading agreements, their welfare will be greater than if no agreements were made. On the other hand, the resulting set of policy decisions will fall far short of being in any sense socially optimal. If the number of voters is not so large as to preclude the formation of partially stable coalitions, it is too small to remove completely the monopsony power a voter will be able to enjoy over any issue of vital importance to him.34
We have explored the role of party in the formation of protocoalitions and vote trading as the device for producing stability of outcomes while avoiding a coalition dominant on all issues. In so doing we reemphasize Madison's point (in The Federalist, Paper no. 10) regarding representative government as a defense against tyranny of the majority.
The monopsony problem is, however, a significant issue in representative government. Cases can be constructed in which, in a single legislature, one legislator with a strong interest in one bill can trade off many other votes to produce a majority for his bill. Notice, however, that to do so he must be in the number of minimum winning coalitions equal to the number of votes he needs on his bill. This is not an inconsiderable constraint, in theory or in practice.
An additional protection from monopsony power is the bicameral legislature--if the districts of the two houses are correctly drawn relative to one another. The point here is not "one man, one vote," since the whole of utility analysis is based on this principle,35 but rather that district lines must be drawn so that representative patterns are significantly different in the two houses. What is advocated strongly by the lower house representative of district A may be safely resisted by the upper-house senator whose constituency includes districts A, B, C, and D. Should a majority of these districts be of the same mind as district A, is not the senator then an advocate also? He is indeed, but if the number of senators is sufficiently restricted (in most senates it is not), this event happens only when a consider____________________