The Russia-Ukraine War (2022) brought an unprecedented degree of unity and scale to the responses to Russia’s invasion among European Union member states and the United States, in a way that was incomparable to their responses to the Georgia (2008) and Ukraine (2014-2022) crises. A weak resolve – the firmness of those responses and the underpinning willingness to incur costs – in the preceding crises may have fostered an expectation in the Kremlin that Washington and European capitals' responses to future aggression would follow a similar path. Hence, this paper examines the challenges for resolve in responding to the Russia-Ukraine War (2022), in order to discourage future aggression. It finds that, throughout the three crises, concerns over escalatory risks and disunity in responses between European capitals and Washington constitute two persistent challenges. Maintaining unity can become increasingly fraught as the economic and political costs increase, especially in countries that have historically held closer cultural and economic ties with Russia.