Richard Neustadt (1960) famously stated, “Presidential power is the power to persuade” (Presidential Power, p. 1). In the intervening years, scholars have argued that presidential power resides on a continuum, from a powerful imperial presidency to a weak imperiled presidency. A resolution to this debate has not been possible because we lack an agreed-upon empirical measure of presidential power. In The Enigma of Presidential Power, Fang-Yi Chiou and Lawrence Rothenberg offer a major advance in this regard, providing a test of three different theories of unilateral action: 1) the unilateral model, based on William Howell’s classic work, Power Without Persuasion (2003), positing that presidents have broad discretion to enact executive orders; 2) the chamber-compliance model, whereby presidential influence is constrained by the chamber median’s ideal point; and 3) the partisan-compliance model, with presidential influence constrained by the majority party median.

Why should Congress have the power to constrain unilateral action? Theoretically, the authors posit that Congress has multiple means beyond legislative fiat, including the ability to delay presidential appointments and to control the legislative calendar and the budget. These are impediments that should challenge presidential power during periods of divided government. Chiou and Rothenberg, therefore, directly challenge Howell’s idea that presidents exert power without persuasion, arguing instead that presidents must bargain and work with Congress.

In challenging Howell, the authors provide a testable theory, as well as a well-developed measure of presidential power. First, their methodology for identifying significant executive orders (EOs) incorporates a greater number and variety of sources than past research and provides a means to check for the potential bias of each source. As such, their data are rich, providing a detailed examination of executive orders and unilateral power. This is a particularly important contribution because there are many different measures of significant orders. Second, the authors provide a theoretically based test of the divided government thesis. That debate has led to the conclusion that divided government is and is not a significant determinant of unilateral action. Chiou and Rothenberg argue that during unified government, presidents face fewer congressional obstacles (such as threats to delay high-level appointments). Hence, consistent with Howell’s previous finding, they hypothesize that presidents should issue more significant executive orders during unified rather than divided government. This hypothesis runs counter to the idea that presidents issue more orders during divided government because the opposition party is not amenable to legislative solutions. Again, addressing this debate, empirically and theoretically, is a major contribution of this work.

The analysis is thorough, complex, multilayered, and fascinating. Initially, the authors pool significant EOs and find considerable support for the partisan-compliance model, while the evidence for the unilateral and chamber-compliance models is thin to nonexistent. This finding supports their hypothesis that not only can Congress limit presidential discretion but it also does so. Hence, elections matter, as do political parties. When the authors break the data into seven policy areas, however, they find that the unilateral model does perform best with regard to unilateral actions related to foreign aid and international affairs, while the partisan-compliance model performs best with most, but not all, domestic policies. They conclude that “the underlying process that generates executive orders is more akin to separation-of-powers bargaining than to a president acting, and daring others to respond, with Congress unable to mobilize due to its own collective action problems or policy gridlock” (p. 118).

Still, there are areas where presidents do have considerable power. In a fascinating empirical investigation of the “two presidencies thesis,” the authors again divide the data, this time examining domestic and foreign policy EOs separately. The analysis provides solid support for the idea that there are two presidencies, with presidents having a greater ability to use unilateral power in an unfettered manner with regard to foreign policy. Alternatively, domestic policy fits with the partisan-compliance model, an indication that presidents are far more fervently constrained in this policy area. Consequently, Chiou and Rothenberg do not refute Howell’s unilateral thesis, but rather confine it to one broad type of policy, while arguing that it is not a good fit with domestic policies. Consequently, the implications of the analysis are important for the further development of presidential theory about presidential power.

In particular, the analysis suggests that Richard Neustadt’s bargaining model still holds when we consider the vast array of domestic affairs. Presidents must work with Congress in a divided government, aware that unrestrained unilateral action can be met by a panoply of legislative mechanisms that can delay or permanently block the president’s larger agenda. Likewise, presidents have greater ability to act unilaterally in a unified government, because presidents and their congressional partisans are more likely to share the same ideological and policy views, although the Trump administration will provide a future test of that thesis, quite possibly during a presidency of “disjuncture” (Skowronek, The Politics Presidents Make: Leadership from John Adams to Bill Clinton, 1997).

Finally, Neustadt’s idea of bargaining and compromise breaks down in foreign affairs. This finding is consistent with Moe and Howell (“The Presidential Power of Unilateral Action,” Journal of Law, Economics and Organization, 15(1), 1999), Howell’s 2003 classic (Power without Persuasion), and Howell and Jackman’s studies (The Wartime President: Executive Influence and the Nationalizing Politics of Threat, 2013). As such, we are beginning to see the outlines of a broader theory of presidential power, one during which bargaining and compromise have their place in American politics, with polarization a period where Congress and the president have less of an ability to enact legislation (largely because there is limited room to bargain), and another during which unilateral power without persuasion is pervasive. And while Chiou and Rothenberg raise doubts about the imperial presidency (IP), their analysis leaves wide open the possibility that the IP is alive and well with regard to foreign policy. Since Arthur Schlesinger’s seminal study (The Imperial Presidency, 1973) was based on the president’s war powers, and with a unilateral approach more viable, scholars, pundits, and citizens still have reason to be concerned about the perils of presidential power in this realm.

Chiou and Rothenberg conclude: “We believe that, when taken in toto, our theoretical and empirical analyses by and large solve the enigma of presidential power in a manner heretofore not recognized by social scientists” (p. 179). While they have gone a long way toward reconciling different perspectives on unilateral power, I do not agree that they have solved the enigma of presidential power. Thank goodness, or what would presidential scholars have to write about in the future? Rather, they have provided a solid theoretical basis for the further study of presidential power; for let us remember, unilateral power is but one piece of the larger puzzle. They also demonstrate that we can reconcile some, and perhaps many, of the disagreements in the presidential literature. So, while the enigma limps along, it is far less enigmatic than it once was.