Any book written about American politics in the last 20 years has had to confront the country’s endemic struggles with partisan polarization. But what if we have missed the bigger issue? In The Other Divide, Yanna Krupnikov and John Barry Ryan reconsider what was once the defining question in studies of political behavior and remind us that as divided as Democrats and Republicans may often appear, Americans are just as, if not more, divided between those who are “deeply involved” and those who are not. Today though, this divide has become destabilizing, self-reinforcing, and foundational to the more visible forms of partisan disagreement. Their argument is theoretically robust and empirically solid. It is provocative and relevant well beyond America’s borders. While the book’s presentation and approach will be most familiar to public opinion scholars, it is necessary reading for Americanists, comparativists, and political theorists alike.

“Deep involvement” is the conceptual glue tying together this comprehensive study, which includes several experiments and multiple representative samples of the American public. At one level, deep involvement is a measurement critique that pushes against the standard way in which scholars have attempted to measure interest in politics and/or knowledge—in short, what is often thought of as democratic capacities. But the measure of deep involvement picks up on something conceptually distinct. Many people follow the news and show up to vote. But they are different from the people glued to their phones, who seek out the significance in the minutiae of congressional procedure, and who feel emotionally invested in the smallest details of political life. These are the obsessed, the politically anxious, the fanatical, the “deeply involved.”

On each of the four dimensions that characterize deep involvement, this book demonstrates how these individuals comprise a vocal and empowered minority—different from the larger subset of Americans who are merely knowledgeable and interested in politics. The deeply involved spend more time following public affairs; they see politics as something profoundly important to their day-to-day lives; they are more likely to share their thoughts about political issues and think that they are fulfilling some important civic function when they do; and they are more likely to have an intense dislike for out-partisans.

Ironically though, while representative samples suggest that a small minority of the American public is deeply involved, these are the behaviors that are most likely to come to the forefront of our collective imagination when we think about the state of American politics, including among the not-so-involved. This is what makes this book’s argument so meaningful, and why this is certainly not a “it’s better than you might think” narrative. Far from it.

It is not just that the deeply involved are different. The deeply involved are overrepresented, and that representation exacerbates the divide among all Americans, not just the deeply involved. Yes, the deeply involved are slightly more likely to partake in traditional forms of political engagement, such as voting in a primary election. Their real influence, however, comes from the fact that media representations of polarization and political disagreement are more likely to focus on easier-to-find, self-promoting individuals who are among the deeply involved. This is a dynamic unlikely to be shaken anytime soon, and it is a root cause of growing distrust and dissatisfaction with the country’s political system. A separate chapter (Chapter 8) on media dynamics relies on interviews and surveys of journalists to demonstrate how the deeply involved—while behaving nothing like the ordinary American—are nevertheless represented as the archetypical democratic citizen, the casual American “on the street” who is angry, anxious, and active. These images are picked back up by majority opinion, creating a self-fulfilling, sticky prophecy of a deeply divided nation.

Connecting the dots between the socialization of deep engagement, its multitude manifestations, and its consequences for media representation of public opinion, this is a path-setting book. It breaks new ground by tilling up old questions about the minority of individuals who care deeply about politics, and each chapter is sure to inspire further study. I’ll note three areas that showcase the argument’s relevance and broad importance and raise important questions for future research in the discipline.

First, although the book is clear to draw clear conceptual boundaries around the term “deep involvement,” some might wonder whether the goal posts for political engagement have been moved a bit. Invoking a definitional example used throughout the book, it is not necessary to be a talented musician, or to even play a single note to be deeply involved in something like jazz music. The same is true about what many might think of as political engagement and its relationship to deep involvement, as defined. But beyond the semantic point as to whether involvement is the right term, diving further into the concept might tease out other paths by which the influence of the deeply involved is enlarged. I am left wondering whether this is all contingent on the rise of the Internet and social media platforms—developments that Berelson, Lazarsfeld, and McPhee (credited with the original study of deep involvement) could not have foreseen. There are undoubtedly other institutional developments, such as the hollowing out of party organizations, which have further elevated the voices of the deeply involved. Representatives, like journalists, also have the finger on the public’s pulse. What are the possible incentives that encourage them to elevate the loudest voices in room? The authors’ own evidence hints at a more streamlined dynamic between party elites and the deeply involved, which takes place outside of the media environment. This is evident from surveying what the deeply involved of both parties say is the most important issue in comparison to the not-so-involved (Chapter 4). The issues that evoke deep involvement are no surprise to anyone that follows—even superficially—American politics: drugs and abortion for deeply involved Republicans; too many guns and racism for deeply involved Democrats. But there are issues among the not-so-involved of both parties: stagnant wages, health care costs, and yes, partisan division. Which one of these issues fits the agenda of both major parties today?

Second, there is a need to further explore the causal pathways that create deeply engaged citizens, within a specific historical-institutional context. Throughout the chapter on socializing dynamics, which are too often ignored in studies of mass attitudes, the authors present several possible alternatives: college attendance, affluence, parental influence. Largely as a result of the authors’ own concerns over causal validity, we do not have a definitive story as to why some people are more likely to become deeply involved in politics. There is clearly a cyclical aspect, where deep involvement “bubbles” encourage desirable in-network behaviors. Why those bubbles are widening awaits deeper scrutiny and longitudinal data unavailable at the moment.

Finally, with its focus on media and the incentives that journalists face, it is easy for professional political scientists to walk away from this book feeling squeaky clean. But this book is a shot across the bow of mainstream political science research. In elevating the political above most else in people’s lives, political science has also played a role in lionizing a potentially misguided type of ideal citizen. It is an open empirical question, but I would guess that political scientists are more deeply involved than average citizens. The book gives us no definitive answer to the question of how involved we should expect democratic citizens to be, nor does it seek to do so. But it presents a number of empirical regularities to show that deep involvement is in tension with other normatively appealing ideas, such as political equality, compromise, and a belief in pluralism.

It is hard to imagine after reading this book that one could take any study of polarization seriously that does not account for variation in political involvement. Theoretically rich and deploying multiple methods, this book will be necessary reading for graduate students, and is written accessibly enough to engage upper-level undergraduates.