How do the changes in the two superpowers’ domestic and international politics affect the prospects for ASEAN-led cooperation over the South China Sea issue? First, it increases the importance of crisis management. Stepped-up US and Chinese deployments will increase the risk of clashes, while decreased US-China economic interdependence will increase the danger of escalation where clashes do occur. Second, it presages greater challenges to ASEAN unity and centrality in the handling of the South China Sea issue. Third, the intensifying rivalry has increased the incentive for China to appear to be a responsible player in the region. Possessing many of the attributes of a regional “middle power,” Vietnam could use its ASEAN Chair role in conjunction with its capable diplomatic network to launch initiatives to stabilize the South China Sea. Broadly, these could include (1) innovations in crisis management, (2) addressing intra-ASEAN disputes, (3) initiating multilateral fisheries management, and (4) facilitating clearer ASEAN positions on great power conduct. However, research indicates that while numerous states possess the capabilities and status quo orientation associated with “middle powers,” the actual adoption of “middle power diplomacy” ultimately hinges on the choices of political leaders.