Over the past four years, ties between Beijing and Pyongyang under Xi Jinping and Kim Jong Un have been on a one-way trajectory: down. While the Chinese president sent a delegation of advisers to Pyongyang shortly after taking office to deliver a personal letter to the North Korean leader, Kim's welcome greeting to his new Chinese counterpart featured a satellite rocket launch in December 2012 followed by a nuclear test in February 2013 during the Chinese New Year and on the eve of Xi Jinping's first National Party Congress.
The provocations marked the first of many that have disillusioned the Chinese leadership (and people) about their fraternal brothers in the North. When Pyongyang tested its fifth nuclear test last week, after having already stolen the world's attention from China's Group of 20 limelight by firing three ballistic missiles, it only added insult to injury.
Under Kim's regime, North Korea has dealt China a steady stream of irritants: the execution of Jang Song Thaek, China's most trusted North Korean interlocutor; a fifth nuclear test and possible development of a hydrogen bomb; multiple long-range missile tests despite senior Chinese diplomatic efforts to halt them; and the testing of a two-stage, solid-fueled ballistic missile most recently, which adds significantly to the North's missile program's capabilities. Even a Chinese leader more inclined to pursue stronger relations with China's traditional ally would have had trouble justifying such efforts in light of these egregious actions.