How robust is public support for extended nuclear deterrence in patron and client states? Recent studies have improved scholarly understanding of US public opinion about nuclear weapon use against non-nuclear adversaries. Yet, there is limited knowledge of public attitudes regarding retaliation for nuclear strikes against US allies. We develop a theoretical typology of nuclear crises and investigate this phenomenon with a novel survey experiment ( n = 6,623). Americans, Japanese, and South Koreans viewed realistic emergency alert messages about a most-likely case for nuclear retaliation: a North Korean missile attack on a US ally protected by the nuclear umbrella. Support for nuclear retaliation is low in all three countries, with important cross-national differences. Favorability increases with North Korean nuclear first-use, but it remains limited nonetheless. Surprisingly, US “tripwire” troop casualties do not increase Americans’ demands for nuclear retaliation. These findings have important implications for the study of nuclear crises and practice of extended deterrence.

2 KAC set their threshold for inclusion at Level 3, or "some major violations." But of the 222 dyads, Morrow and Jo code 173 as Level 1, or "no violations at all." Three are Level 2, or "minor violations." Nine are Level 3, and twenty are Level 4, or "many violations such that compliance doesn't matter." Seventeen were undetermined due to missing data.

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Brendan Green and Austin Long make a signiªcant contribution with their theoretical framework for peacetime signaling of clandestine military capabilities. 1 Examining U.S. anti-submarine warfare (ASW) during the Cold War, they argue that choices to disclose capabilities depend on uniqueness (replaceability) and anticipated countermeasures (pp. 59-60). Green and Long cannot fully account for many historical cases, however, because they overlook decisionmaker concerns about the spread of technology. A modiªed framework combining their theory with fears of technological diffusion offers greater predictive power by explaining the broader dilemma of revealing military innovations during both war and peace.States conceal military capabilities to avoid two threats: nulliªcation and duplication. 2 Green and Long's variables of uniqueness and countermeasures focus on the former while failing to address the latter. Green and Long argue that if the risk of countermeasures is low or if replacement capabilities exist, signaling becomes attractive for "improved general deterrence, adversary resource diversion, and diplomatic concessions or strategic adjustments" (p. 56). Duplication is a fundamentally different concern. Disclosures may provide an adversary with insights to improve their own capabilities. The fear of nulliªcation identiªed by Green and Long does not preclude concerns about technological diffusion (pp. 51-52).