The election of Donald Trump posed an existential challenge to NATO. At the end of his tenure, however, the US president had neither withdrawn membership nor substantially undermined the alliance from within. This article helps explain the puzzle of why NATO survived Trump's presidency. Extant explanations emphasize domestic factors such as the US foreign policy machinery and entrenched liberal ideology, structural reasons and Trump's idiosyncratic personality. While these accounts possess some explanatory value, they remain incomplete as they omit one central factor: NATO's leadership. Drawing on more than twenty original interviews with senior officials, the article demonstrates that particularly Secretary-General Stoltenberg's strategic responses were a necessary factor in changing Trump's stance on burden-sharing and helped maintain a robust deterrence policy toward Russia. These findings carry important implications both for theoretical debates on international organizations' agency in fending off contestation and policy debates on which actors shape NATO by emphasising the hitherto understated role of the secretary-general.