The nuclear weapons taboo is considered one of the strongest norms in international politics. A prohibition against using nuclear weapons has seemingly shaped state behavior for nearly seven decades and, according to some observers, made nuclear use ‘unthinkable’ today or in the future. Although scholars have shown that nuclear aversion has affected decision-making behavior, important questions about the nuclear taboo remain unanswered. This article seeks to answer a basic question: How durable is the taboo? We develop different predictions about norm durability depending on whether the taboo is based primarily on moral logic or strategic logic. We use the comparable case of the norm against strategic bombing in the 20th century to evaluate these hypotheses. The logic and evidence presented in this paper suggest that the norm of nuclear non-use is much more fragile than most analysts understand.