Signaling virtue: legitimacy, reputation, and NATO’s strategic communications during the war in Ukraine

International organizations (IOs) heavily rely on their public image, investing resources to enhance legitimacy and reputation. This article advances a conceptual framework integrating these two dimensions to analyze how IOs respond to external security crises through public digital diplomacy (PDD). We focus on NATO’s strategic communication efforts amid Russia’s full-scale invasion of Ukraine in February 2022, arguing that the crisis prompted intensified signaling toward prospective members, with an emphasis on Finland and Sweden, whose accession would greatly enhance NATO’s capabilities. Drawing on an interpretive discourse analysis of over 800 NATO Tweets and Facebook posts published between February 2021 and May 2022, from the lead-up to the invasion through Finland and Sweden’s membership application, we identify three membership signaling strategies: professionalism and capability, credibility and integrity, and normative legitimacy. To assess the resonance of this signaling, we examine public opinion trends and elite political discourse in Finland and Sweden during the same period. Our findings suggest a constitutive interaction between NATO’s crisis PDD communications and the domestic environment in both countries. The results highlight how legitimacy and reputation are actively projected during periods of organizational insecurity, with enlargement-related signaling playing a key role.