Audience costs theory posits that domestic audiences punish political leaders who make foreign threats but fail to follow through, and that anticipation of audience costs gives more accountable leaders greater leverage in crisis bargaining. We argue, contrary to the theory, that leaders are often unaware of audience costs and their impact on crisis bargaining. We emphasise the role of domestic opposition in undermining a foreign threat, note that opposition can emerge from policy disagreements within the governing party as well as from partisan oppositions, and argue that the resulting costs differ from audience costs. We argue that a leader's experience of audience costs can trigger learning about audience costs dynamics and alter future behaviour. We demonstrate the plausibility of these arguments through a case study of the 1863–4 Schleswig-Holstein crisis. Prime Minister Palmerston's threat against German intervention in the Danish dispute triggered a major domestic debate, which undercut the credibility of the British threat and contributed to both the failure of deterrence and to subsequent British inaction. Parliament formally censured Palmerston, contributing to a learning-driven reorientation in British foreign policy.