This study examines how ROK-U.S. extended deterrence credibility discourse evolved (2013-2024) amid North Korean nuclear threats and U.S. administration changes, and its impact on alliance power dynamics. Using critical discourse analysis of Security Consultative Meeting texts, the research reveals how credibility is discursively constructed within asymmetric political contexts. The analysis illuminates how power asymmetries manifested differently across administrations: as institutionalized stability under Obama, transactional uncertainty under Trump, and reconstructed partnership under Biden. These discursive shifts both reflected and enabled South Korea’s changing security approach. The evolution suggests South Korea’s gradual transformation from a more dependent position to an active participant in deterrence architecture, while navigating complex power dynamics within the alliance framework.