The US federal government since the mid-twentieth century is the political science discipline’s most frequent case study. And yet its fascinating trajectory is often treated as mere background for current events, rather than as a unique story merging broad political patterns and specific historical developments. Bryan D. Jones, Sean M. Theriault, and Michelle Whyman’s new book, The Great Broadening, tells its familiar and important narrative with substantial new insight because it synthesizes the large-scale dynamics of the political system’s substantive focus.

The federal government massively broadened in policy-making scope in the 1960s and 1970s, presaging a conservative backlash, partisan and ideological polarization, and a move from congressional lawmaking to oversight. From 1961–76, Congress passed many more important laws than usual—and nearly all political indicators show a bulge of activity around that time. The action was largely bipartisan and occurred across the policy spectrum. This activist era is reflected in the permanent new institutions that it built and the expansive new vision of national government that it endowed us.

The Great Broadening shows that this extensive lawmaking led to a largely permanent expansion of the national policy agenda: it both brought new social problems and issues to government’s attention and deepened the scope and scale of its engagement with existing issues. The agenda expansion was visible in the topics of legislative hearings, bills, and budgets. A conservative backlash was able to stop the growth of the agenda but not to reverse it. The national government thus still pursues myriad goals in differentiated policy pockets.

The expansion had two key consequences for Congress. First, it passed fewer but larger bills, addressing many different topics at once and leaving most policy-making details to agencies. Second, it stopped holding many hearings on bills or new legislative ideas and shifted to executive branch oversight. Despite Congress’s burgeoning role in maintenance, these changes made it less an institution for developing new policy and more a forum for grandstanding.

Polarization came after the broadening, largely led by conservatives (with the Republican Party moving steadily rightward starting in 1978). The interest group explosion also came in its wake, with most groups fighting to protect existing benefits or stop new regulation, rather than calling for new policies. Republicans, who had been partners in the expansion, became more opposed to new initiatives and more critical of the inherited policy structure. Policies of the broadening era created the bureaucracies and constituencies to remain sustainable, but not to continue expanding indefinitely. As a result, groups pushing for change are now more likely to have stable opponents and partisan sides.

The Great Broadening helps fill in the gaps between research on policy making and political parties. Like the initial broadening discussed in the book, theories of policy making also tended to start out largely nonpartisan. But it is clear in retrospect that much of the policy development they tracked was dependent on Republican acquiescence, which has now become much harder to count on. The long success of liberal policy making eventually undermined conservative cooperation—and Republicans have become less interested in maintaining the enlarged system.

The Great Broadening is structured as an outline of this phenomenon, followed by an evaluation of its potential causes and then a review of its many consequences. The methodological discussion is admirably clear in articulating both the reasons why broad social research over decades is necessary and the inevitable downsides that come from the macro-level approach. Social scientists, the authors remind us, should not pretend that variables such as election outcomes, interest group organizing, or the content of media coverage have relatively constant influence on the political system over time. Instead, we have experienced and cataloged one particular history. In the only version we have, many different influences came together at once and enduringly changed what came afterward.

Scholars nonetheless have to work with the evidence available—and the incredible team of Jones, Theriault, and Whyman have assembled copious data to document the key trends and evaluate their potential antecedents and implications. Scholars who work in any particular policy area or subset of US policy-making institutions should not lose sight of the big picture. Analyzing the development of energy or health policy without seeing it as part of a general expansion and stalemate would be incomplete, for example, just as tracking the workings of agencies or lobbying firms without noting their provenance would shortchange the foundational role of policy.

Given such a broad political transformation, however, any monocausal explanation is likely to fall short. Although Jones, Theriault, and Whyman are cognizant of the many important factors driving change, they concentrate on the role of social movements, especially protests surrounding civil rights, in coaxing the political system to broaden. I remain deeply skeptical of this explanation. Protest activity certainly coincided with the policy-making period, but (as always) it is difficult to tease out causal forces with time-series plots alone.

Congress expanded its policy action in many areas that were not the subject of substantial protest and did not draw from demands of broad social movements. Like interest group development, many social movements followed (rather than led) associated policy innovation. In addition, analogous broadening was occurring in other global political systems less tied to the US civil rights movement.

The book does usefully dispel other theories based on single explanatory factors, such as critical elections, partisan majorities in Congress, and public opinion trends. But as with the role of protests, it is difficult to see the broadening reaching its full potential without these background factors also being present. Political science should also give the internal actors of the time period real agency in bringing about the expansion: many experienced presidents, legislators, and group leaders are widely credited by historians for working out passable compromises.

Despite the complexity of understanding causes, The Great Broadening has important lessons for contemporary politics. First, although keeping an issue off an agenda has long been seen as the critical second face of power, nearly everything is now on the political agenda in some form. The challenge for activists and policy entrepreneurs is instead fighting for attention against nearly everyone else to raise the salience of one issue among many, even for minor revisions updating prior policies.

A second key lesson is that scholars and policy makers must be attentive to the many layers of policy that are now our inheritance. For example, even with a flowering of new policy ideas in the 2020 campaign season, the actual stimulus bills recently debated in Congress tended to include long lists of incremental adjustments to prior policies alongside their headline initiatives. Any new policy idea has to enter the thicket of current laws and institutions.

Although The Great Broadening itself is focused on Congress, it should also persuade political scientists to give more attention to the bureaucracy and subnational governments. Jones, Theriault, and Whyman have (perhaps inadvertently) illustrated why much of the action is no longer in Congress. If the agenda is already wide (and if Congress can barely update the many government functions it has already initiated), much of the innovation is likely to come in administrative rulemaking and state and local implementation.

The Great Broadening is an impressive synthetic achievement. It tackles macro-level questions with grace and attention to detail. It constitutes proof that political science can still add a new perspective, even about the institutions and periods scholars have studied most closely.