The US has always reserved the right to use military force to save strangers – unilaterally, if necessary. Yet successive US Administrations have perceived this right as an option to intervene, and not as a general duty toward endangered civilians that is exercised in a more or less consistent fashion. The responsibility to protect is thus a double-edged sword for the United States: on the one hand, it legitimises the use of military means as a last resort to protect civilians from the worst human rights abuses. On the other hand, however, it limits US freedom of action by establishing clear guidelines for the use of force and by creating an expectation to act when human rights are being violated on a massive scale and all other non-military means have been exhausted. Unsurprisingly then, US engagement with the responsibility to protect has been rather ambivalent. This article reviews the Bush Administration's position on R2P in theory and practice, taking the Darfur crisis as a showcase of the Bush Administration's wavering commitment to atrocity prevention. The second part of the article discusses whether the Obama Presidency has departed from the Bush Administration's approach and assesses to what extent it will provide new impetus to the development of R2P.