Abortion stirs heated passions among many US citizens and legislators; moreover, many people think of it as an all-or-nothing issue on which there is little middle ground. So it is all the more surprising that members of the US House of Representatives tend systematically to support incremental, rather than major, changes in federal abortion policy. This is the puzzle at the heart of Scott H. Ainsworth and Thad E. Hall's significant book about the making of abortion policy in Congress.

The authors' solution to the puzzle centers on a theory of legislative decision making that predicts that House members who care about changing abortion policy will tend to support incremental changes as a strategic response to the constraints and incentives they face. (Of course, representatives sometimes offer bills that propose nonincremental changes for symbolic reasons, knowing that the bills have no chance of passage; Ainsworth and Hall note this but are interested in genuine attempts to change policy.)

Factors inside and outside of the House cause this “strategic incrementalism.” The internal factors consist of the imposing legislative hurdles to be overcome if any bill is to become law. The thrust of this part of the theory is that enacting any new law is extremely difficult and incremental proposals have a better chance of passage than nonincremental proposals: Incremental changes are generally acceptable to more legislators than are proposals to adopt larger policy changes and are also less likely to generate serious legislative opposition. An incremental proposal thus has a better chance of successfully navigating the committee, party, and separation-of powers obstacle course of the legislative process. The external factors have to do with pleasing constituents in order to be reelected. The authors posit that for a variety of reasons (discussed later), incremental proposals are more likely than nonincremental proposals to bolster legislators' reelection chances. A House member who wants to change policy thus has a strong incentive to propose moderate changes.

Abortion Politics in Congress is methodologically diverse. Its theory is grounded in congressional literature but also draws from other disciplines; it uses insights from formal legislative models, but merges them in an innovative manner with ideas not typically incorporated into formal models. The book also includes an array of qualitative and quantitative evidence to support the theory and to help make sense of abortion policymaking.

One consequence is that the book works on a number of levels and offers something for many different audiences. It is a nice, accessible primer on the history of abortion policy and politics in the United States, including the history of abortion legislation in Congress. It is also an introduction to the procedural and electoral imperatives that shape congressional behavior generally—and it is a case study of congressional policymaking on a deeply contentious issue.

Readers with strongly held beliefs about abortion or who are otherwise interested in the issue, but who are not very familiar with Congress, will likely come away with a deeper understanding of why Congress tends to adopt incremental policy and perhaps also with a greater appreciation for the systemic reasons why even committed pro-life and pro-choice legislators have strong incentives to support incremental policy changes. Many people have a limited understanding of Congress and experience frustration when it produces incremental policy changes that fall short of expectations. Anecdotally, it seems that people often blame such shortcomings on the individuals serving in Congress at that moment. One lesson of this book is that such shortcomings are less a function of individual congresspersons and more a function of their environment than is often supposed.

Another strength of the book is that its appeal and accessibility is unrelated to a reader's position on the abortion issue. The authors strive to make no normative judgment about abortion (or, for that matter, about Congress). The tone is analytical and they avoid using the kinds of loaded language that typifies much of the public discourse regarding abortion. Readers who approach abortion from a normative perspective may find it surprising—and will hopefully find it refreshing—to read a study on abortion that approaches the topic from a dispassionate perspective. Certainly, they will find it different from much of what is said and written about the subject.

The book will also appeal to many public policy scholars. In addition to some of the reasons already mentioned, it will appeal to this audience because of its emphasis on incrementalism as a general topic, regardless of the policy issue. Ainsworth and Hall discuss the concept in depth, including its past ascendancy and decline in the public policy literature. They explicitly seek to revive the concept. The book revolves around three topics—abortion policy, congressional policymaking, and incrementalism. Each seems to take the spotlight at different times and at several points one gets the sense that the authors are at least as interested in incrementalism as a topic unto itself, as in the other two topics.

In the end, though, this work is primarily about congressional behavior in the context of abortion policy and the foremost audience will likely be congressional scholars. More specifically, its biggest audience will likely be those who study congressional policymaking (although the book has broad implications regarding institutions and representation that will appeal more broadly).

Multiple aspects will be of interest to these readers—especially the ways in which the book pushes the envelope on theories of congressional decision making. While many aspects of the theory are standard in the literature, others are novel and somewhat unorthodox. They will likely spur changes in the thinking of some readers and will just as likely spur skepticism or disagreement from others.

For example, the authors emphasize an unusual aspect of spatial models of legislatures. In most such models, it is taken as a given that a legislator's goal is to maximize the size of his or her policy gain on a particular issue; implicitly, it is also taken as a given that he or she will be more than happy to win with the barest possible majority in order to achieve this goal. Spatial modelers' reflexive focus on the median voter underscores these assumptions. By contrast, Ainsworth and Hall emphasize that there is a trade-off between maximizing the size of the policy gain and maximizing the vote margin on passage of a bill. In other words, a smaller policy gain can achieve a larger vote margin.

That trade-off does not matter if legislators do not care about vote margins. But the authors go on to posit that members of Congress do in fact value larger majorities for two general reasons: They increase the odds of passage and they decrease the odds of an electoral backlash among constituents. Along the way, the book makes unconventional assumptions about legislators' risk aversion and about the electoral effects of a bill passing by a large vote margin, among other things. These ideas are provocative in every sense of the word: They are intriguing, they are clever, they challenge some widely used conventional modeling practices, and they will generate a range of reactions from congressional scholars. It is well worth a look for all of us interested in modeling legislative decisions.