This paper has two purposes. First, it attempts to explore why the U.S. will not abandon South Korea despite the Trump Administration was reluctant to provide support to South Korea. Second, this paper illustrates the values of the U.S.-ROK alliance to the security on the Korean Peninsula and the U.S. presence in the "Indo-Pacific" region. To achieve these goals, this paper will extract four variables from Victor Cha's "Powerplay" theory. In this paper, the author argues that the U.S. will not abandon South Korea, no matter a Democratic or a Republican to be the U.S. president. It is because the U.S. still needs to prevent North Korea from provoking the U.S. and the U.S. relies on South Korea to ensure its presence in the "Indo-Pacific" region.