A long-standing narrative in U.S. engagement policy toward China draws a tacit causal link between engagement and Beijing’s socialization into the U.S.-led liberal international order (LIO).1 Amid recent decreasing faith in engagement, this article constructs a framework tailored to explaining the conditions for China’s state socialization into the hegemonic order when the U.S. tries to engage China. It contends that the socialization of a still-rising China is an arduous cause that hinges on four conditions: the accommodation of China’s interests in international institutions, the existence of a problematic situation, status recognition, and the absence of obstacles to domestic internalization. To test the socialization premise, the article applies the framework to a theoretically most-likely case of China’s socialization—U.S. post-2009 engagement with China on global climate governance. It finds that despite some ambiguous signs of state socialization, China’s adoption of the U.S.-promoted co-leader identity was primarily rooted in domestic changes in interest perception and was thwarted by domestic obstacles—economic development and energy security—to the internalization of the idea of Chinese climate leadership.