State legislative redistricting receives far less attention from political scientists than congressional redistricting. This is a bit puzzling since legislative redistricting actually far better fits the overwhelmingly negative perception of the line-drawing process because, in this instance, politicians are, in fact, drawing their own districts. Members of the U.S. House of Representatives have to rely on the goodwill of their co-partisans back in their state legislatures for advantageous districts. Jonathan Winburn's new book provides a glimpse into the politics of legislative districting. The central thesis of the book is that state-level rules imposed on the districting process do as much, if not more, to prevent gerrymandering than the partisan make-up of the state government. For instance, if a state requires that district lines minimize the number of split counties, or if a state uses nested districts (where upper chamber districts are composed of two or more lower chamber districts), the possibility of unfair district lines is much less than if a state just tries to rely on a so-called “neutral commission” to draw electoral boundaries.

The book develops a typology to examine how partisanship affects redistricting: (1) unified partisan control of the state government, (2) divided partisan control of the state government, (3) partisan commission, and (4) neutral commission. For each of these types, the author uses two states as case studies. The book does a nice job laying out traditional districting principles and some of the major federal laws and Supreme Court cases that also affect the districting process. One small problem I had was that the book could have more clearly laid out how the Voting Rights Act affects the process. For instance, the author writes, “The VRA is not applicable in either Idaho or Washington” (p. 41), but this is only true for section 5 of the VRA, which applies to some states and not others. Section 2 of the VRA applies to the entire country.

The book is nicely structured, with each chapter having similar sections that link the intentions of the mapmakers to electoral outcomes. In order to try to detect whether or not a gerrymander took place, the book takes various approaches, like classifying what kinds of districts existed in the baseline plan (safe majority, competitive, etc.) and then comparing the newly drawn districts to the old districts. So, if the majority party is trying to pack and crack the minority, we expect that safe majority-controlled districts will probably be made less safe as the majority party tries to more efficiently spread their votes across more districts. This approach is simple and intuitive, but it will not necessarily always pick up the asymmetry that defines a gerrymander. For instance, if the current map (the one in place for the last decade) is gerrymandered and there are minimal changes made for the new map, the comparison of current districts to past districts will make it appear that the new map is tame, when nothing could be further from the truth. I would have preferred to see a bit more rigorous analysis, like using Gelman and King's JudgeIt software, to analyze the underlying fairness of the districts.

The case studies for divided partisan control really highlight the fact that what tends to happen in a divided state legislature (where each party controls one of the chambers) is that rather than having more neutral districts, the majority party in each chamber draws their own gerrymandered plans and then defers to the other chamber for their electoral boundaries. New York was not one of the case studies, but having spent some time in that state, it was evident to me that this is exactly what happens there as well. For better or worse, this process simply institutionalizes divided government. Each of the case studies is very well researched and I learned a great deal about the politics of redistricting in all of these states.

One item that struck me in reading the book is that the redistricting process helps explain why partisan realignments are “trickle-down” affairs—as a region realigns from one party to the other, it tends to happen from the top (presidential) downward (to state and local). There is a really nice example from Texas, where they use a legislative redistricting board as a backup to the state legislature for drawing legislative boundaries. The board comprises elected statewide officials, so in order to complete the realignment toward the GOP (the lower chamber of the state legislature was controlled by the Democrats until 2002), the Republicans first had to win a majority of the statewide offices.

Ultimately, this work shows that redistricting can have significant effects on the elections that follow, but it is also possible for redistricting to be relatively benign or even have the opposite electoral impact of what the redistricters intended. Winburn shows that the rules and constraints that are placed on those who seek to redistrict limit their ability to draw electoral boundaries to make the kind of naked partisan grab that we typically think of when we think about the process of redistricting. While there are no major theoretical breakthroughs in this book, it is a solid contribution to the field, and those interested in redistricting and state politics ought to read it.