Motivated Reasoning or Cooperative Internationalism? Ideology and Public Responses to International Endorsements

Do reactions from international organizations or foreign authorities persuade domestic public opinion? While many studies argue that individuals’ ideological orientations condition their responses to international organizations, two competing mechanisms explain this effect. The cooperative internationalism perspective suggests that left-leaning individuals, who value multilateralism, are more receptive to international reactions. In contrast, the motivated reasoning perspective posits that individuals accept international reactions consistent with their ideological predispositions and reject those that are not. Distinguishing between these mechanisms is empirically difficult because international reactions often align with left-leaning positions. We address this challenge by examining Japan’s decision to discharge treated cooling water from the Fukushima Daiichi Nuclear Power Plant into the Pacific Ocean. Although left-leaning Japanese citizens were skeptical of the discharge, several international organizations and foreign governments expressed support for it. Using data from an original 2024 online survey of over 1,100 Japanese respondents, we find that endorsements from the International Atomic Energy Agency and the United States increased support for the discharge among left-leaning individuals. These results support the cooperative internationalism perspective over motivated reasoning, suggesting that the internationalism posture of the ideological left can shape responses to international society.