This article argues that Trumpism intensifies a reflexive crisis of legitimacy in global AI governance. Legitimacy in global governance rests not on sovereign command but on justificatory claims that are continuously contested. Drawing on Zürn’s (2018) concept of “reflexive legitimation conflict,” the analysis shows how disputes extend beyond institutional performance to contest the very criteria of rightful authority. In AI governance, where institutions remain fragmented and weakly institutionalised, this conflict is particularly acute. The Trump administration’s 2025 AI Action Plan redefined legitimacy around sovereign discretion, deregulation and technological nationalism, delegitimising liberal norms of ethical oversight and multilateral coordination. By contrast, China has sought to reposition itself as a steward of multilateralism and developmental inclusion, aligning open-sourcing and UN-centred proposals with claims of ethical authority. Through discourse analysis of US and Chinese strategies, the article demonstrates how AI governance exemplifies pluralised and antagonistic legitimation in a post-hegemonic order.