In their book, Helen V. Milner and Dustin Tingley examine the effect of domestic politics on the capacity of American presidents to conduct diplomatic and military affairs. They develop a theory of distributive politics to explain domestic mobilization around executive policies and provide extensive empirical analysis of key influences, which include interest group lobbying, congressional appropriations and roll calls, bureaucratic structure, and public opinion. They demonstrate that political activity and public attitudes vary in predictable ways across diverse policy instruments in response to the economic and ideological interests arising under each approach. The authors succeed admirably in overturning conventional wisdom that the president enjoys a relatively free hand in foreign affairs, a feat that earned Sailing the Water’s Edge the American Political Science Association’s 2016 Gladys M. Kammerer Award. Milner and Tingley fall short, however, in proving their contention that domestic constraints lead to the militarization of U.S. foreign policy.

The study of domestic politics is not new to international relations. Theorists have focused on audience costs as restraints on conflict initiation and have identified institutions as fostering cooperation among democracies. Researchers also have looked at influences on specific U.S. foreign policy events, such as public opinion, congressional oversight, media coverage, interest-group activity, and bureaucratic behavior. Milner and Tingley’s contribution is to integrate theory and observation in a project that is unprecedented in scope.

The authors contend that presidents enjoy multiple instruments to promote U.S. security abroad and favor those involving the least interference from domestic actors. The greatest domestic pushback, they argue, arises from policies with visible, concentrated, economic costs and benefits or ideological differences, which include trade, economic aid, immigration, and domestic military spending and, to a lesser extent, sanctions. Milner and Tingley further posit that political actors have fewer incentives to engage the executive about geopolitical aid and troop deployments, because such instruments have the characteristics of collective goods and also offer less information about likely impacts (pp. 36–38). Four empirical chapters, one each for interest groups, members of Congress, federal agencies, and citizens, analyze the level of political activity for each policy type.

The array of data the authors bring to the task of deconstructing the domestic politics of U.S. foreign policy is extraordinary. In Chapter 4, for example, they show how distributional instruments affect support for the president’s position on all foreign policy votes from 1953 to 2008, as well as on roll calls by individual lawmakers on a subset of policy votes between 1979 and 2008. In Chapter 6, the authors provide experimental evidence that the public credits Congress with having better information than the president about policy instruments with distributive consequences, such as trade, immigration, and economic aid. In Chapter 5, they repurpose data on bureaucratic structure to reveal greater congressional control over foreign policy programs with distributive outcomes from 1946 to 2012. In Chapter 3, they examine hundreds of thousands of observations for lobbying efforts between 2007 and 2014 from the digitized reports filed by groups under the Lobbying Disclosure Act in order to discern which policy tools are targeted by various groups. Taken together, these chapters reveal striking similarities in the patterns of political activity: instruments with strong distributional characteristics stimulate the greatest level of political engagement.

Comparison across categories of actors is limited, however, because many of the data sets do not match up with the seven policy instruments. Chapter 3 on lobbying considers witness testimony on trade, economic aid, geopolitical aid, troop deployments, and sanctions, but not immigration or domestic military spending. It examines whether groups bypass the White House, but only with four of the seven categories. In Chapter 6 on public opinion, the authors’ own survey about which branch controls a policy tool omits sanctions, while several of the Cooperative Congressional Election Studies about citizens’ priorities among economic aid, geopolitical aid, and military deployments leave out trade, immigration, sanctions, and domestic military spending. Consequently, Milner and Tingley are unable to ascertain which political actors are most effective in constraining the president, whether they augment their influence by targeting similar instruments, or when they alter White House policy.

The lack of comparability poses a more difficult challenge for the authors’ contention that meddling by domestic actors induces presidents to adopt military deployments instead of “softer,” potentially more appropriate, instruments. They offer a case study of sub-Saharan Africa during the Clinton and George W. Bush administrations to probe for such substitution effects. They contend that both presidents preferred policies of economic aid and trade, but deemphasized these tools in favor of military options after repeated political conflicts: Clinton with the African Crisis Response Force (ACRF) and Bush with the U.S. Africa Command (AFRICOM).

Sub-Saharan Africa probably is not the best venue for examining policy substitution. The stakes for the United States in the region have been comparatively low; moreover, Milner and Tingley’s narrative provides grounds for a different interpretation. Both presidents, but particularly Bush, enjoyed success with nonmilitary instruments, and neither initiated the use of troops in the region. Indeed, Clinton succumbed to congressional and public pressure to rescind his orders to expand the peacekeeping effort in Somalia launched by his predecessor, George H. W. Bush; he endeavored to ignore Rwanda; and he adopted a restrained response to the bombings in Kenya. Bush, who continued to promote a modest trade agenda throughout his presidency, avoided the use of force on the subcontinent and embraced the idea of a unified command at the urging of key senators. It is not clear that the conflict experienced by these presidents over aid and trade were any more severe than difficulties they encountered with their domestic agendas. In addition, their respective decisions to beef up the command structure in the region arguably resulted from concerns about the growing threat of terrorism, rather than frustration with political conflict over economic instruments.

The theory of policy substitution remains vitally important to views of executive power in foreign affairs, even if Milner and Tingley cannot confirm it. The authors fear that presidents will choose military options, not because they are most effective but because they inspire less domestic political conflict. From the vantage point of hindsight, this perspective seems problematic on two counts. First, Barack Obama opted for diplomacy over force in places like Iran and adopted a mix of instruments with respect to Iraq, Libya, Syria, or China. He undoubtedly would be surprised to learn that his decisions regarding the projection of American military power around the globe were unconstrained by domestic politics. Second, the authors appear to regard domestic influence on U.S. foreign policy as dangerous in undermining the capacity of presidents to pursue liberal internationalism. In the view of many scholars, however, unfettered presidential power has been the greatest danger to American security both at home and abroad. The skeptics, including me, would like to see more domestic conflict about the means and ends of U.S. foreign policy, not less. The fact that Milner and Tingley find so much domestic political activity about matters beyond the water’s edge provides a ray of hope, therefore, for those who worry about an imperial presidency.