A thorough reassessment of how domestic factors do and do not constrain the use of American military force abroad in the early twenty-first century. More than two decades have passed since the September 11th terrorist attacks resuscitated debates about the “imperial presidency” within the United States. During that same time, the United States has fought costly and inconclusive wars in Iraq and Afghanistan, pivoted to the Pacific to counter China, and pulled its gaze back to Europe and the Middle East in response to wars in Ukraine and Gaza. Moreover, new technologies and ways of funding and staffing wars have made the costs of war less visible to the public while polarization has increased and a new legal doctrine of presidential power has gained force. Against this backdrop, Checking the Costs of War reassesses how domestic factors have both constrained and failed to constrain the use of military power across different contexts and over time. Richly empirical chapters explore the varying effects of different kinds of potential checks: legislative, public opinion, and bureaucratic. Collectively, chapters offer new insight into the prospects for war and peace today.