|As nationalist sentiments gain traction globally, the attitudinal and institutional foundations of the international liberal order face new challenges. One manifestation of this trend is the growing backlash against international courts. Defenders of the liberal order struggle to articulate compelling reasons for why states, and their citizens, should continue delegating authority to international institutions. This article probes the effectiveness of arguments that emphasise the appropriateness and benefits of cooperation in containing preferences for backlash among the mass public. We rely on IR theories that explain why elites create international institutions to derive three sets of arguments that could be deployed to boost support for international courts. We then use experimental methods to test their impact on support for backlash against the European Court of Human Rights in Britain (ECtHR). First, in line with principal-agent models of delegation, we find that information about the court's reliability as an 'agent' boosts support for the ECtHR, but less so information that signals Britain's status as a principal. Second, in line with constructivist approaches, associating support for the court with the position of an in-group state like Denmark, and opposition with an out-group state like Russia, also elicits more positive attitudes. This finding points to the importance of 'blame by association' and cues of in/out-group identity in building support for cooperation. The effect is stronger when we increase social pressure by providing information about social attitudes towards Denmark and Russia in Britain, where the public overwhelmingly trusts the Danes and distrusts the Russians. Finally, in contrast to Liberal explanations for the creation of the ECtHR, the study finds no evidence that highlighting the court's mission to promote democracy and international peace contains backlash. We show that the positive effects of the first two arguments are not driven by pre-treatment attitudes such as political sophistication, patriotism, internationalism, institutional trust or political preferences.