When the United States goes to war, the nation’s attention focuses on the president. As commander in chief, a president reaches the zenith of power, while Congress is supposedly shunted to the sidelines once troops have been deployed abroad. Because of Congress’s repeated failure to exercise its legislative powers to rein in presidents, many have proclaimed its irrelevance in military matters.

After the Rubicon challenges this conventional wisdom by illuminating the diverse ways in which legislators influence the conduct of military affairs. Douglas L. Kriner reveals that even in politically sensitive wartime environments, individual members of Congress frequently propose legislation, hold investigative hearings, and engage in national policy debates in the public sphere. These actions influence the president’s strategic decisions as he weighs the political costs of pursuing his preferred military course.

Marshalling a wealth of quantitative and historical evidence, Kriner expertly demonstrates the full extent to which Congress materially shapes the initiation, scope, and duration of major military actions and sheds new light on the timely issue of interbranch relations.

Throughout American history, presidents have shown a startling power to act independently of Congress and the courts. On their own initiative, presidents have taken the country to war, abolished slavery, shielded undocumented immigrants from deportation, declared a national emergency at the border, and more, leading many to decry the rise of an imperial presidency. But given the steep barriers that usually prevent Congress and the courts from formally checking unilateral power, what stops presidents from going it alone even more aggressively?  The answer, Dino P. Christenson and Douglas L. Kriner argue, lies in the power of public opinion.

With robust empirical data and compelling case studies, the authors reveal the extent to which domestic public opinion limits executive might. Presidents are emboldened to pursue their own agendas when they enjoy strong public support, and constrained when they don’t, since unilateral action risks inciting political pushback, jeopardizing future initiatives, and further eroding their political capital. Although few Americans instinctively recoil against unilateralism, Congress and the courts can sway the public’s view via their criticism of unilateral policies. Thus, other branches can still check the executive branch through political means. As long as presidents are concerned with public opinion, Christenson and Kriner contend that fears of an imperial presidency are overblown.