“As close as lips and teeth” is how Mao Zedong famously described China’s ties with North Korea.

Chinese President Xi Jinping’s visit to Pyongyang was a reminder that the old saying — which captures shared history and geographic proximity — still holds. But it also revealed something else: North Korea has become a far more difficult partner for China to manage.

The Chinese president arrived to an elaborate welcome on Monday, complete with a 21-gun salute and soldiers chanting wishes for his good health. Kim Jong Un and his wife greeted Xi at the airport — but beyond the pomp and pageantry is a much bigger question: How much influence does he still have over the North’s mercurial leader?