Prime Minister Shinzo Abe's summit with U.S. President Donald Trump reinforced the security guarantees iterated by U.S. Defense Secretary James Mattis on his visit to Japan and South Korea the week before. Trump's explicit support for Japan has partly allayed concerns over the United State's security commitment to Japan and the region by sending a clear message to the U.S.' alliance partners in Northeast Asia that the U.S. remains committed to the Japan-U.S. alliance.
Moreover, strong messaging concerning North Korea's ICBM and nuclear development, an explicit reiteration that the Senkaku islands fall under security guarantees of Article 5 of the Japan-U.S. security treaty and an overt condemnation of China's perceived unconstructive behavior in the East China and South China Seas has left Japan and other Northeast Asian countries, for better or worse, with a much clearer picture of their bilateral relations going forward under a Trump presidency.
Noticeably absent from the discussions during Abe and Mattis' visits, and in Trump's East Asian strategy, has been any mention of Southeast Asian countries, in particular, those that have territorial disputes with China in the South China Sea. The oblique references to the July 2016 ruling by The Hague's Permanent Court of Arbitration, which rejected Chinese sovereignty claims in the South China Sea, during discussions in Japan offered little to smaller countries in Southeast Asia with no capacity to counter China's perceived assertive behavior in the disputed waters.