Academics, especially political scientists, have provided a wide range of empirical evidence of increased polarization (particularly among elites) in American politics. Our own work outlines this polarization against the entire backdrop of American history, but what has been missing from recent political science work has been a focus on micro-level mechanisms operating in the modern era. Belying the great quantity of empirical evidence is a black box of “elites” that have polarized over time. What we do not see, or observe, or have evidence for is exactly the process by which these elites (and which ones particularly, if any) have systematically driven the two parties toward their currently polarized ideologies.

Sam Rosenfeld fills this gap by providing a detailed account of these micro-level processes. Using a vast array of archival sources, he documents how polarization is largely the result of the initiative of a few key individuals wishing to instill national ideological unity in the parties in the face of competing pressures for local constituencies.

Rosenfeld begins with what E. E. Shattschneider described as the goal of moving political thinking away from the issue-oriented Progressive approach (with an emphasis on independence from parties) toward using parties as vehicles for making policy that reflected ideological priorities (p. 14). Comparing this vision to the decentralized, ideologically overlapping party organizations of the 1950s, Shattschneider’s work culminated in the oft-mentioned American Political Science Association report Toward a More Responsible Two-Party System (1950). The report formally outlined the case for a pair of responsible parties with distinct, cohesive, ideological visions that give voters competing alternatives.

Such intellectual ambition needed to be matched by practical efforts within the parties themselves, however. As Rosenfeld’s narrative moves through the 1950s and into the 1960s, he demonstrates how the confluence of civil rights as a cross-cutting issue (p. 46) combined with internal goals for realignment among a subset of party insiders (p. 62) and led to a unique opportunity to reshape the political parties. This transitioned politics away from a system reflecting the midcentury values of collegiality, compromise, deference, and bipartisanship (p. 42), where, according to Thomas E. Dewey, “the resemblance of the parties [is] the very heart of the strength of the American political system” (p. 64), to one in which parties could begin to diverge and adopt unique positions, especially as issues became places where parties could gain electoral benefits (p. 126).

Rosenfeld demonstrates the myriad of organizations required to bring life to such an ideological vision. He documents the growth in the Democratic Party of the Democratic Advisory Council (p. 35), the Students for a Democratic Society (p. 95), and finally the Socialist Party (p. 224), with each move bringing Democrats closer to an ideological alignment away from centrist policies and toward a unified liberal party position. For their part, Republicans grew even more strategic in their infrastructure, establishing the Local Elections Campaign Division (p. 201) and other offices to coordinate electoral efforts around the surging party brand. In fact, each party’s best creations (of ideological unity through interest groups like the Americans for Democratic Action, or the previously mentioned electoral infrastructure) were often mirrored by the opposition, creating a pair of parties driven by the other’s ingenuity and process.

Over time, this drive for ideological cohesion, matched by the other party, culminates in an “additive, multidimensional contemporary polarization” (p. 281), where parties have increasing incentives to take distinct positions across all issues, not just a subset of them. This is reminiscent of Geoffrey C. Layman and Thomas M. Carsey’s world of “conflict extension,” where parties take polarizing positions across a variety of issues without allowing conflict to dissipate on prior issues (“Party Polarization and ‘Conflict Extension’ in the American Electorate,” American Journal of Political Science 46(4), 2002).

Rosenfeld’s archival work here is revealing. We get an in-depth look at the individuals who create extraparty organizations (like the Democratic Advisory Council, p. 35), a reading of competing political approaches to regional party differences (p. 70), the individual architects of ideological party positions in the 1970s (p. 97), even a tracking of the convention-level conflicts that shaped the trajectory of presidential nominations throughout the 1970s. The tapestry he weaves is particularly rich; he pulls direct quotations from a myriad of primary material to help buttress the overall lineage of polarization. It is also particularly attractive, as no data exist to test such a micro-level theory over time, especially in the 1960s and 1970s. Gallup and other surveys ask the rare question about ideology (which the author notes as well), but evidence on the ideology of the mass public in these years is notoriously scant. And similar survey evidence on the ideology of elites in the party organization is nonexistent.

We offer a few ways in which this work might be improved and extended. Rosenfeld might more clearly delineate the key political entrepreneurs or moments in his timeline. The very breadth of the historical work makes it difficult to discern key moments or figures on the path to polarization. Put differently, it is clear that the figures he outlines in the two parties played some role in polarization, but it is difficult to discern precisely who played a crucial role.

The second is a consideration of the events as well as people involved in this process. Our own work demonstrates the importance of exogenous shocks (like the Great Depression and the 1970s stagflation) in creating opportunities for entrepreneurs to mold and shape the ideological direction of the parties. While Rosenfeld places a remarkable amount of attention on individuals, he pushes events and circumstances to the margins. But they deserve our attention, as only the confluence of circumstances and entrepreneurs leads to polarization.

Our third suggestion is for the inclusion of a more thoughtful consideration of the cast of characters in the modern age (regarding maintenance of brand, depolarization). Rosenfeld offers an intense portrait of the “black box” of the 1950s, 1960s, and 1970s, but relatively few modern characters are outlined. This is important as we try to chart the ideological trajectory of the modern parties. For example, our own work suggests outsized roles for Milton Friedman, Paul Weyrich, Ronald Reagan, Newt Gingrich, and others. Further, our recently published work (B. Dan Wood and Soren Jordan, “Presidents and Polarization of the American Electorate,” Presidential Studies Quarterly, 48(2) 2018) suggests that presidents in general have been very important to the polarization of the American electorate. In other words, “polarization” is an idea of distinct and cohesive parties in opposition, but in and of itself it does not determine or define the positions the parties take; political entrepreneurs do.

This bleeds into a more general criticism: We walk away from the book with relatively little understanding of exactly what the parties are aiming toward. Both Republicans and Democrats are described as working toward becoming programmatic parties that deliver on a set of ideologically cohesive party positions. But we fail to get a strong sense of what those positions are, outside of “liberal” and “conservative.” Rosenfeld devotes quite a bit of time to the importance of civil rights and the “social issue” (p. 126) in providing the opportunity to form polarized parties, but once parties form as a result of the issues, there is relatively less time and space devoted to the party endgame. To be sure, he notes the various coalitions inside of the Democratic Party (p. 259), and describes the Republican focus on taxes and economics (p. 207). But having so thoroughly detailed the importance of individuals with ideological vision for the creation of polarized parties, it would have been doubly interesting to hear the ultimate ideological vision that these individuals had for their respective parties.

Lastly, Rosenfeld gives quite the bleak outlook for polarization moving forward. Noting the march toward ideological conflict that the parties have undergone in the preceding 50 years, he writes that “the plausibility of new actors being able to effectively reverse that process, either through force of will or procedural tweaks, seems hard to credit” (p. 283). Yet this seems a potentially mistaken conclusion, as the rest of the work serves to show the value of individual agency, even of specific, single persons, in charting the course of the two parties. Rosenfeld even notes this in the same sentence, coming to the conclusion that we just quoted after noting “this book’s emphasis on the agency of historical actors” (p. 283). Why is this agency only limited to the past? Can entrepreneurial members of today’s parties not also look at the contemporary landscape—unpopular Congress, executives, politicians—and find room to capitalize on the opportunity to win electoral victories by making the party less ideological and confrontational? Can exogenous shocks not move parties back toward a state of depolarization? Is not party polarization a dynamic process that rises and falls with the ebb and flow of long-term American history, as has occurred multiple times since 1789?

To be sure, we are not advocating for this movement, or even for a depolarization of the parties. But it certainly seems misleading to suggest that the agency and vision of individuals to chart the course of the parties and to reform their ideological positions is limited to a time when those individuals envision a pair of polarized parties only. To the contrary, that is precisely the contribution of Rosenfeld’s work: outlining the dream of some politicians, intellectuals, or party officials to have cohesive parties offering distinct alternatives. But some other industrious individuals could just as equally have a dream of midcentury values of collegiality and bipartisanship and work to implement them. So it is worthwhile, but demanding, to reflect on the ideological proclivities of the entrepreneurs who shaped our modern parties. That is exactly what Rosenfeld has accomplished in this volume for an earlier era of American politics.