The dominant view in proliferation research holds that security guarantees from nuclear patrons reduce client states’ incentives to pursue nuclear armament. Yet in South Korea, public support for indigenous nuclear capabilities remains high despite strong trust in US extended deterrence. Drawing on the “better-now-than-later” logic from preventive war theory, we argue that this support reflects public forward-looking pessimism about the security environment, shaped by perceptions of the relative decline of the US and North Korea’s advancing nuclear capabilities. Analysis of the 2023 EAI Public Opinion Poll shows that concerns about systemic power shifts and pessimism about future inter-Korean relations are significantly associated with support for nuclear armament. South Korean public assessments of US extended deterrence and North Korea’s military threat do not align with conventional alliance theory expectations that high trust in extended deterrence should reduce support for nuclear armament. These findings underscore the need for reassurance strategies that address enduring alliance credibility.
