To what extent are political leaders entitled to violate embedded moral and legal rules in response to national emergencies? Do they have a duty to do so? This article assesses two prominent liberal approaches to this question. The 'dirty hands' thesis insists that there is a radical separation between private and public ethics and that the latter may require the commission of acts prohibited by the former. A 'lesser evil' approach holds that leaders may even violate the more permissive public ethics if there is a consequentialist case for doing so. Both suggest to some extent that certain acts remain wrong but may be necessary nonetheless. While this position makes good philosophical sense, it makes little political sense. In practice, societies choose either to validate or reject the legitimacy of certain acts. This article aims to overcome this problem by suggesting a new way of thinking about the way that 'dirty hands' and 'lesser evil' ethics work in practice through Ian Clark's work on legitimacy. It argues that in particular cases actors evaluate between competing political, ethical and legal claims, a point illustrated by a brief case study on the torture debate.