The ROK–US alliance is the bedrock of South Korea’s national security and the “linchpin” of US security architecture in Asia. But its origin was characterized by fear and distrust due to the asymmetric power relation between the two allies, and South Korea constantly feared being abandoned by its bigger ally. Yet when the country developed economically and democratized, a new tension emerged, as the new democratic elite, the “386 generation,” chafed at the constraint of the alliance that in its view curtailed inter-Korean dialogue and could entrap South Korea in an unwanted conflict with North Korea or China. The tension accelerated under President Trump as South Korea experienced fear of both entrapment and abandonment, with Trump questioning the alliance and extended deterrence while also decoupling from China, South Korea’s largest trading partner. The crisis of credibility that Trump precipitated is for now stabilized with the change of administration in Washington, but if the US alliance policy changes again then South Korea will look beyond the alliance for enhanced security, including going nuclear, for which there is consistent public support.