We analyze the first large-scale, randomized experiment to measure presidential approval levels at all outcomes of a canonical international crisis-bargaining model, thereby avoiding problems of strategic selection in evaluating presidential incentives. We find support for several assumptions made in the crisis-bargaining literature, including that a concession from a foreign state leads to higher approval levels than other outcomes, that the magnitudes of audience costs are under presidential control prior to the initiation of hostilities, and that these costs can be made so large that presidents have incentive to fight wars they will not win. Thus, the credibility of democratic threats can be made extremely high. We also find, however, that partisan cues strongly condition presidential incentives. Party elites have incentives to behave according to type in Congress and contrary to type in the Oval Office, and Democratic presidents sometimes have incentives to fight wars they will not win.