This article employs a three-pronged approach to test competing theories regarding the size of coalitions required for passing legislation prior to the adoption of cloture in the Senate. We compare predictions generated by a model derived from the theory of pivotal politics with those generated by the theory of universalism. To test these predictions, we first examine coalition sizes on the passage of significant legislation. Second, we analyze the size of coalitions on dilatory motions as a predictor of success in defeating legislation. Finally, we examine coalition sizes on tariff legislation to assess the degree to which politics in this policy area were majoritarian. We find that a pivotal politics-based model incorporating the median voter and veto pivot generally outperforms universalism in explaining lawmaking patterns in the pre-cloture Senate. Narrow majorities were quite successful at legislating, although minority obstruction fostered uncertainty about the threshold required to force a final vote when adjournment loomed.