Public opinion toward foreign adversaries shapes and constrains diplomatic options. Prior research has largely relied on sentiment analysis and survey based measures, providing limited insight into how sustained narrative changes (beyond transient emotional reactions) might follow diplomatic engagement. This study examines the extent to which high stakes diplomatic summits shape how adversaries are framed in online discourse. We analyze U.S.-North Korea summit diplomacy (2018-2019) using a Difference-in-Difference(DiD) design on Reddit discussions. Using multiple control groups (China, Iran, Russia) to adjust for concurrent geopolitical shocks, we integrate a validated Codebook LLM framework for framing classification with graph based discourse network analysis that examines both edge level relationships and community level narrative structures. Our results reveal short term asymmetric persistence in framing responses to diplomacy. While both post level and comment level sentiment proved transient (improving during the Singapore Summit but fully reverting after the Hanoi failure),framing exhibited significant stability: the shift from threat oriented to diplomacy oriented framing was only partially reversed. Structurally, the proportion of threat oriented edges decreased substantially (48% -> 28%) while diplomacy oriented structures expanded, and these shifts resisted complete reversion after diplomatic failure. These findings suggest that diplomatic success can leave a short-term but lasting imprint on how adversaries are framed in online discourse, even when subsequent negotiations fail.