As U.S. President Barack Obama seeks a united front to denuclearize the Korean Peninsula, he's facing an unlikely spoiler: Japan.

Traditionally, China has played this irksome role. The six-party talks over North Korea's nuclear program — suspended since 2009 — never got anywhere largely because China refused to put the screws on its ally. No matter how many missiles the Kim Dynasty fired off, how many nuclear tests it conducted, or how many North Koreans starved or ended up in prison camps, China remained convinced that the alternative of a possible regime collapse was worse.

Yet even the Chinese are now fed up with the antics of North Korean leader Kim Jong Un. Officials in Beijing have openly chastised the North for its provocative behavior and have supported United Nations sanctions against the country. At their one-on-one California summit, Obama and Chinese President Xi Jinping found more common ground on the issue than ever before. Most dramatically, China Construction Bank Corp. ended business with North Korean lenders Korea Kwangson Banking Corp. and Golden Triangle Bank — a slap across the face for strapped Pyongyang.