In the early 2000s, Republican Tom DeLay of Texas held the majority whip position in the U.S. House of Representatives. Nicknamed “the Hammer” and known for playing hardball to get fellow Republicans to toe the party line, he was the most visible party whip in at least a generation, and helped popularize the conception of party whips as enforcers who maintain discipline in no small part through intimidation.

In his impressive new book about party whips in Congress, Lawrence Evans wants to disabuse us of that conception and replace it with a far more nuanced view of whips’ diverse jobs. More importantly, he wants his readers to understand some of the important inside politics that substantially affect congressional decision making. Along the way, he provides valuable insights into relationships among representation, lobbying, parties, and lawmaking.

A primary motivation for studying whips is that, as the linchpins between party leaders and other party members, their behavior can tell us not only about leaders’ and members’ goals but also about the power relationship between leaders and members. Studying whips can thus shed considerable light on debates about the distribution of power within Congress.

Evans jumps feet first into long-running debates about parties’ influence over lawmaking, arguing that the literature’s heavy reliance on spatial game-theoretic models has led scholars to miss some important aspects of leaders’ power and to overstate other aspects. He takes particular exception to spatial models’ assumptions that members of Congress have complete preferences over all choices, and that those preferences are exogenous to the lawmaking process. Arguing that preferences are incomplete, often undefined, and derive from multiple sources (including party whips), he hopes to “convince scholars . . . to rethink how they have come to conceptualize lawmaking in Congress, particularly the roles played by parties and leaders. Far more attention . . . needs to be devoted to the processes through which individual members form preferences and positions on legislative issues, and perhaps less to anecdotes about arm-twisting and the manipulation of procedure” (p. xvi).

As an alternative to assuming complete and exogenous preferences, the book offers a “behavioral” framework rooted in such classics as David Mayhew’s (1974) Congress: The Electoral Connection and Richard Fenno’s (1978) Home Style. Members have multiple goals that lead them to try to please various “audiences” (constituencies)—especially inside the district, but also some outside the district, such as lobbyists or activist organizations. A member’s preference on a particular issue or vote results from the array of preferences among these audiences, and how the member weights each.

One of Evans’s main arguments is that the array and weighting of audience preferences strongly affects the potential for party leaders to influence a member’s preferences on a given vote. He articulates four possible ideal-type arrays of preferences to make claims about how different arrays systematically shape leaders’ power: Roughly speaking, with disinterest, a member’s audiences care little about the issue, leaving the member free to follow party leaders’ wishes. With consensus, audiences are in agreement, and so party leaders have limited ability to influence a member’s vote. With generalized conflict, audiences disagree, leaving a member uncertain how to vote—and creating opportunities for party whips to sway the member. Finally, with cross pressure, a member’s audiences favor one course of action but party leaders want the opposite; this is when whips are most likely to go to the greatest lengths in attempting to shape a member’s decision.

Because whipping uses scarce resources, however, leaders decide strategically when to whip a question or issue, largely reserving it for votes that are close. Other factors that affect leaders’ choices are the size of the party, actions of the other party, presidential involvement, and polarization. Leaders are sometimes able to sway members’ audiences to the party position, thereby indirectly shaping a member’s vote choice. But one of Evans’s major claims is that constraints on whips and leaders impede their ability to induce support from members.

The book emphasizes whips’ informational role within their parties: Much of their job is to serve as information conduits between leaders and members, most notably by conducting whip polls in which they survey party members about their positions on a prospective vote, by conveying leaders’ goals to party members, and by conveying party members’ concerns or objections to leaders. Another role is to bargain on behalf of leadership; when whips sway members’ votes, it often happens via agreements in which the whips offer side payments or concessions to members, rather than through coercion or intimidation.

This is easily the most extensive study of whips ever undertaken, in no small part because whip poll data and many documents illustrating the workings of the whip system have never before been assembled on this scale. One of Evans’s accomplishments is to have collected data on roughly 1,500 whip polls, as well as countless memos and other documents, from former members’ papers in archives around the country. Combining those materials with personal interviews and the accounts of others, the author presents an unprecedented look inside the whip process. The book prioritizes quantitative methods in some chapters and qualitative methods in others, but always intermixes them to good effect. Much of the second half of the book is devoted to four chapters that take close looks at whipping during four different time periods, respectively: the “Textbook” period (1955–72), the period of growing individualism (1973–82), the period of reemergent partisanship (1983–94), and the era of Republican majorities (1995–2002). These chapters offer vivid portraits of the ways that whipping has worked at different times and how it has evolved. Although The Whips is mostly about the House, there is also a chapter about the Senate.

Readers will occasionally find the distinctions between behavioral and spatial models to be too sharply drawn, relying on narrow constructions of spatial models. For example, at one point Evans asserts that “legislative deviations from centrist viewpoints in the chamber . . . have become the sine qua non for [empirically demonstrating] party influence” (p. 45)—which overlooks the breadth of studies of parties’ effects in Congress. And in some places, the tone suggests that the behavioral and spatial models are mutually exclusive, while in other places it treats them as compatible. Clearly, some elements of Evans’s behavioral perspective and elements of spatial theories complement each other; in fact, one of the exciting things about this book is that it lays a strong foundation for future theoretical advances that combine different approaches. These are minor criticisms, though, that do not undermine the work’s main points about preferences being incomplete and endogenous to the lawmaking process.

The foregoing barely scratches the surface of the book’s content or contributions; unfortunately, space constraints preclude more detailed discussion here. But the book is densely packed with findings and arguments that either augment or contravene conventional accounts of party power—such as the claim that making party votes “explainable” to members’ audiences is one of party leaders’ most significant sources of leverage, or the finding that whips were actually quite effective during the supposedly weak-party Textbook Congress period. A close read offers many fascinating and intriguing insights into Congress’s decision making. And, in the end, The Whips constitutes a worthy guide to anyone seeking to better explain congressional decisions.