China’s heightened prominence and the unpredictable nature of U.S. involvement in Asia exacerbates existing fissures across Southeast Asia. Both regional arrangements like the Association of Southeast Asian Nations (ASEAN) and individual regional states are facing greater pressure as a result. Tacking between Beijing and Washington is becoming trickier for Southeast Asian governments. Common ground within ASEAN is increasingly difficult to establish given the highly disparate nature of its membership. This spells a decline in ASEAN’s ability to exercise initiative and autonomy. The grouping runs the risk of losing its ability to buffer U.S.-China competition. This implies that Southeast Asia can potentially turn into either a front for US-China contestation or a region that is less welcoming of an active U.S. presence. To avoid such outcomes, Southeast Asian governments need to engage seriously with ASEAN reform or grapple with the possibility of alternative arrangements—including those involving extra-regional partners. However, a combination of domestic distractions, the promise of immediate returns from China’s Belt and Road Initiative, and uncertainty over the U.S. role in the region mean that there is limited political will to move in these directions. Should the United States have an interest in continued engagement with Southeast Asia, it may have to do so in a more unstable and less accommodating environment.