When does a nucleararmed state's provision of security guarantees to a militarily threatened ally inhibit the ally's nuclear weapons ambitions? 1 The security model of nuclear proliferation argues that by providing extended deterrence to an insecure client, a patron obviates the client's need for indigenous nuclear weapons capabilities. 2 Underpinning this argument is the logic of "nuclear dependence," which posits that clients will prefer to delegate their security to a patron to avoid the risks associated with nuclear acquisition. For clients facing military threats, however, uncertainty about the durability and credibility of a patron's protection means that security guarantees are imperfect substitutes for independent capabilities. As a result, clients are compelled to minimize risks to their survival by pursuing both security guarantees and nuclear weapons of their own.Critics of the security model contend that this indeterminacy in its logic indicates that security guarantees cannot explain nuclear restraint, and that competing causal variables are necessary to account for client states' nuclear choices. In particular, past scholarship has largely turned to domestic factors to explain the choice of external reliance versus nuclear weapons acquisition, including the politico-economic preferences of a country's ruling coalition, the popularity of nonproliferation norms, the psychology of political leaders, and the prevalence of domestic actors with a veto over nuclear decisions. 3 These