(CNN) Secretary of State John Kerry's diplomatic hot streak faced a major reality check Wednesday. He landed in Beijing aiming to convince a reluctant China to ratchet up pressure and punishments on its recalcitrant nuclear-armed ally North Korea. But the limits of American influence with a rising regional giant, questions over just how much influence even China has over North Korea's unpredictable behavior and the administration's own ebbing time and political capital make the chance of meaningful progress on one of the word's most vexing security threats a long shot. That doesn't mean Kerry, who has made a habit of what some see as solitary, quixotic diplomatic endeavors, isn't trying.Washington has long seen Beijing as holding the most meaningful card when it comes to changing Pyongyang's behaviorBut China, despite its increasing annoyance with North Korea, is apparently unsure of how to control Kim's erratic regime
Kerry described _ to reporters this weekend as a "clearly reckless and dangerous, evolving security threat in the hands of somebody who is questionable in terms of judgment and has proven thus to China."