Congress has not declared war since June 5, 1942, when it did so against Bulgaria, Hungary, and Romania during World War II. Yet, since then, the United States has been involved in multiple military conflicts, both large and small. Despite repeated uses of force, the reluctance of members of Congress to use their formal power to declare war, or at least to invoke the 1973 War Powers Resolution, appears to demonstrate that they have effectively delegated their war powers to the president. Not only has their behavior seemingly rendered the term “congressional war powers” oxymoronic, but their refusal to accept responsibility for use-of-force decisions has also contributed significantly to the perception of a “preeminent presidency” when it comes to foreign policymaking.

No one should deny that presidents are typically the single most influential U.S. foreign policymaker, and their constitutional role as commander in chief gives them wide sway over the use of military force. Still, presidents worry about whether Congress will support their decisions to use force. Presidents and other administration officials ask questions: Will Congress support this? If not, how can congressional support be gained and what will it cost? Simply put, members of Congress must be playing some role in the decisions to send forces in harm's way. Thus, the goals of the authors in this study are to determine both the roles played by Congress in presidential use-of-force decisions and the policy consequences of those roles.

Certain circumstances do not lend themselves to a robust congressional role. There may be little incentive for Congress to act if majority party control of Congress is tenuous, the use of force is quite small in nature or can be swiftly completed before Congress can act, or the international situation demands a U.S. military response. Thus, Congress cannot be expected to play a significant role unless three conditions are met: the majority party is both large and fairly cohesive ideologically, the use of force is major in scope and duration, and the use of force is discretionary and not mandated by the political or security situation.

The authors employ a variety of methodological approaches to check these expectations. For example, event-count models demonstrate that partisanship matters mightily, but only when the stakes are raised. From 1945 to 2000, larger majorities in Congress for the presidential party mean more major presidential uses of force, and vice versa. The impact of partisanship washes out when all uses of force—both major and minor—are considered. Obviously, presidents can do largely as they please when the use of force is small in scale and short in duration.

Relying on a data set of 15,004 opportunities to use force, the authors again find that partisanship matters. The larger the opposition party in Congress, the longer the president will wait between the opportunity arising and the actual deployment of troops. Presidents also wait longer to respond militarily when the target is an ally of either the United States or Soviet Union or when the volume of trade between the United States and the target state is high. Thus, when decisions are dominated by such realpolitik concerns as alliances and economic considerations, the impact of domestic politics recedes—and vice versa.

After the extensive examination of quantitative data, the authors then turn to case studies to flesh out the analysis by examining 1954 Indochina, 1981–88 Nicaragua, 1982–84 Lebanon, 1989 Panama, 1992–94 Bosnia, and 1998–99 Kosovo. Their findings reconfirm the importance of domestic variables. In almost every case in which the president “confronted members who had reasonably well-defined views about how operations should proceed, if they should proceed, and members who stood poised to lash out should a military venture falter … the president adjusted course” (p. 149). In most instances in which members intervened in a use-of-force decision, it was after the forces had actually been committed. However, public statements made by members of Congress before the deployment of troops served to strengthen (or weaken) the president's hand in dealing with an opponent, while negative public statements in particular primed the media and the public for the tough questions to ask should events turn out badly.

Returning again to quantitative analysis, the authors found that both national and local journalists listen to congressional critics of a presidential use of force. Members of Congress thus can generate more media coverage—whether positive or negative—of a use of force. Notably, their commentaries to local news outlets play an important role in shaping local public opinion about a use of force, and national public opinion represents the aggregation of such local opinion.

Employing multiple methodologies, this nuanced study demonstrates that while presidents face minimal congressional constraints over minor uses of force, the timing of major use-of-force decisions depend on the partisan composition of Congress and the degree to which members of Congress shape both media coverage and public opinion. Presidents are routinely forced to anticipate congressional concerns and to react appropriately to them—often building congressional viewpoints into the administration's position. Consequently, the idea of presidents anticipating the reactions of members of Congress and accommodating them in advance should give pause to scholars who think that congressional roll-call votes are the only measures of legislative influence.

More broadly, While Dangers Gather is an important contribution to the small but growing literature that sees Congress as an underappreciated foreign policymaker. Scholars such as James Lindsay (Congress and the Politics of U.S. Foreign Policy, 1994), Rebecca Hersman (Friends and Foes: How Congress and the President Really Make Foreign Policy, 2000), and Ralph Carter and James Scott (Choosing to Lead: Understanding Congressional Foreign Policy Entrepreneurs, 2009) show that through the use of informal powers, Congress as an institution or members of Congress as individuals can shape U.S. foreign policy in important ways that scholars often overlook. William Howell and Jon Pevehouse add to this argument by showing that on the issue most often cited by those who see the president as the preeminent U.S. foreign policymaker, Congress influences presidential decisions to use force, how to use those forces, and when to use those forces, and ultimately, Congress may also play a role in determining whether those use-of-force decisions are seen as successful.

Washington's policy practitioners already know these things, but many academics fail to realize them because such informal policymaking influence is not easily measured. Because it addresses a question so central to the study of foreign policymaking and answers that question so well, While Dangers Gather has garnered significant recognition. It was the corecipient of the 2008 Richard E. Neustadt Award given by the American Political Science Association's Presidency Research Section, as well as the recipient of the 2007 D. B. Hardeman Prize from the Lyndon Baines Johnson Foundation. This nuanced study of how presidents and members of Congress interact to shape use-of-force decisions deserves a careful read by all who study executive–legislative interactions in foreign policymaking. If Congress matters more than many academics have thought when it comes to something as important as war powers, where else may congressional influence be underestimated?