Even by the standards of a rogue nation, North Korea's recent behavior has been outrageous. First, it tested a solid-fuel medium-range missile to demonstrate its rapidly expanding arsenal of dangerous weapons. Then it reportedly dispatched a team of assassins to kill Kim Jong Nam, the half-brother of the country's ruler, in Malaysia. There seems little doubt that Pyongyang was behind the murder. Either way, the brazenness of the assassination, which involved the use of the deadly nerve agent VX in an international airport terminal in Kuala Lumpur, has shocked the world.

Amid growing international pressure to punish North Korea for its flagrant violation of international law, no country faces as acute a dilemma as China, Pyongyang's long-time patron. Beijing also served as the protector of the hapless Kim Jong Nam who, until his murder, had taken refuge in the Chinese gambling enclave of Macau.

For Beijing, North Korea under the rule of Kim Jong Un has become more of a strategic liability than an asset. Since Kim Jong Un assumed power in 2011 after the death of his father, Kim Jong Il, he has purged senior officials with close links to China and accelerated Pyongyang's nuclear and missile programs. In the last five years, North Korea has conducted three nuclear tests and has touted its advances in increasing the destructive power of its nuclear devices and developing long-range ballistic missiles.