Derek Grossman is a senior defense analyst at the think tank RAND Corp. in Santa Monica, California, and an adjunct professor in the practice of political science and international relations at the University of Southern California. He formerly served as an intelligence adviser at the Pentagon. Southeast Asia's premier regional bloc -- the Association of Southeast Asian Nations (ASEAN) -- is in trouble once again. Malaysia, the current chair, wanted to forge unity and act collectively to respond to American tariffs. Instead, select ASEAN members -- including Cambodia and Vietnam -- have decided to pursue bilateral trade negotiations to protect their own interests.