Coalitional Politics and Logrolling in Legislative Institutions

We examine how a foresighted legislative chamber will design its institutions in response to ex ante incentives for universalism and ex post incentives for minimum winning coalitions and what coalitions will form as a result. To do so, we develop a model of vote trading with an endogenous voting rule and coalition formation process. We find that in equilibrium, legislative chamebers will almost never choose institutions that guarantee either simple majorities or universalistic outcomes. Rather, coaltion sizes from minimal winning to universalistic will be possible under certain conditions given the choice of voting rule. Further, these coalitions will be “minimally necessary,” just large enough to sustain cooperation.