Does a patron state's hardline posture reassure the public in an allied state?

How does a great power ally's demonstration of toughness toward a common adversary influence the sense of security among its weaker ally's citizens? The literature on the effects of standing firm against adversaries has significantly evolved in recent years, but empirical evidence is scarce, especially at the mass level. By taking advantage of the unique opportunity of the 2019 North Korea–US Hanoi summit, we examine the conditions under which a powerful alliance partner's firm and uncompromising posture toward a common adversary reassures the citizens of a junior ally. Based on alliance literature, we hypothesize that a patron's hawkish policy reassures its protégé when the protégé fears abandonment more than entrapment and that the more a citizen of the protégé fears abandonment, the more reassuring the patron's hawkish policy is to the individual. Our analysis of online surveys conducted before and after the summit using a quota sample of the Japanese electorate shows that the level of threat perception is significantly lower in the post-summit sample than in the pre-summit one, especially among the respondents who fear abandonment by the US. We thus conclude that President Trump's decision not to compromise with North Korea on its nuclear programs alleviated Japanese citizens’ concerns about US alliance commitments to Japan, improving their security perception. This study is significant in showing that a patron state's policy toward a common adversary can greatly influence the perception of its ally's citizens as well as its government.