Filling the Amendment Tree: Majority Party Control, Procedures, and Polarization in the U.S. Senate

Harry Reid is often lauded by fellow Democrats as one of the most powerful Senate Majority leaders in modern history. One tactic that he used to usher in legislation was a parliamentary procedure known as “Filling the Amendment Tree.” Amendment trees are diagrams that demonstrate the amendment process for legislation, but Reid often limited the number of amendments that could be offered on a piece of legislation using this procedure. From the majority’s perspective, this procedure helps usher in legislation and protects vulnerable moderates from having to vote on controversial legislation. Still, others argue that the restrictive procedure limited the ability of moderate Democrats to distinguish themselves from their party leadership, making them vulnerable to attacks. In this article, I find that filling the amendment tree did not limit moderate Democrats from proposing amendments. In fact, although moderate Republicans shied away from the process of filing amendments in protest, there was no statistical relationship between ideology and the number of amendments filed for Democrats. Still, upon examination of voting data, the use of the procedure homogenized the voting records of moderate Democrats in the 112th and 113th Congresses. Furthermore, it forced moderate Republicans to vote more often with the Democrats in each of the Congresses in which Reid employed the procedure