Recent empirical work has brought a renewed attention to the effect congressional rules of procedure have on the size of winning coalitions. Specifically, scholars have posited that legislative success hinges on the support of legislators identified by institutionally defined decision rules. Under these theories, supermajority decision rules in the U.S. Senate lead to larger, more inclusive coalitions on final passage. In this article, I reevaluate these claims by controlling for changes in the legislative agenda and the roll-call voting record. I find that the aggregate size of winning coalitions is highly responsive to the underlying legislative agenda, the size of the Senate's majority party, and the manner in which researchers treat unrecorded votes. Further, my findings suggest that any connection between changes in the Senate's voting rules and the size of winning coalitions is spurious.
Eric Schickler and Gregory J. Wawro have authored a response to this article, and Anthony J. Madonna has authored a rejoinder to this response. Both are available as Supporting Information.