Senator Jim Jeffords left the Republican Party in May 2001 and became an independent. Because he agreed to vote with the Democrats on organizational votes, this gave that party a 51–49 majority in the Senate.

Using the “Jeffords switch,” Chris Den Hartog and Nathan W. Monroe examine how power is shared and transferred in the Senate, as well as whether Democratic bills became more successful after the switch. They also use the data after the switch, when the Republican Party still held a majority on many Democratic Party-led committees, to examine the power of the committee chairs to influence decisions. While the authors find that the majority party does influence Senate decisions, Den Hartog and Monroe are more interested in exploring the method and limits of the majority party to achieve its goals.

Chris Den Hartog is Professor of Political Science at California Polytechnic State University.
Nathan W. Monroe is Professor of Political Science and Tony Coelho Endowed Chair of Public Policy at the University of California, Merced.

“A worthy professional contribution to the literature on the Senate, this book advances the debate on how parties make a difference in the Senate, and Congress more generally, with important new perspectives and empirical findings. Den Hartog and Monroe’s inclusion of case study and elite interview material provide richness and welcome nuance to the analysis.”
—Bruce Oppenheimer, Vanderbilt University

“A splendid example of scholars taking advantage of a natural quasi-experiment in a creative way, combining quantitative, qualitative, and case-study materials to weave a nuanced and compelling narrative. I think it will be a visible and well-cited contribution to the literatures on Congress and quasi-experimental design.”
—Walter Stone, University of California, Davis

“This creative new book on the Jeffords Switch offers a nuanced examination of the role of majority parties in structuring outcomes in the U.S. Senate, since the authors have a chance to “hold everything else constant” in their analysis within the same Congress.”
—Jamie L. Carson, University of Georgia

"In The Jeffords Switch Den Hartog and Monroe provide a thoughtful, well-argued account of the how the Senate majority party uses the tools at its disposal to push forward its legislative agenda. ... Drawing on a variety of methods, the authors challenge the standard accounts of minimal majority party influence in the Senate by demonstrating the majority party’s ability to secure the outcomes it favors. Recommended."
-- CHOICE

"The book illuminates the nuts and bolts of structure and operation in the Senate, analyzing each piece and step individually, showing the ways that these aspects changed (or did not) after the Jeffords switch. Almost every reader is likely to find an assessment of the particular motion or outcome that interests them." - Thomas R. Gray, Congress the Presidency