The Thai ruling elites ostensibly desire to embrace China’s Belt Road Initiative (BRI), but why has this not resulted in more extensive engagement with the BRI? Why has BRI project implementation in Thailand been extremely slow despite the elites’ public pledges? This article addresses this puzzle by arguing that the gap between the pledges and slow project implementation stems from the deep contestation for authority and legitimacy between two sociopolitical coalitions: a conservative faction clustered around the palace, the military, the Democrat Party, and the yellow shirts and a faction centered on former leader Thaksin Shinawatra. Both sides generally favor engaging China for pragmatic purposes. There is little disagreement over whether or not to build a high-speed railway. Rather, the issues are how best to pursue and implement this project, how China should be involved, and which parties the project should benefit. The two camps have repeatedly modified the railway’s construction plan to appeal to their different support bases. In addition to political opposition, such long-standing contestation has encouraged bureaucratic foot-dragging, which undermines the progress of the project, especially when the government suffers from a deficit in democratic legitimacy.