U.S. President Joe Biden last week asked his Chinese counterpart, Xi Jinping, if he could try to talk North Korea out of a new nuclear weapon test but he acknowledged that he did not know if China had the capacity to do so.
As unpredictable North Korea builds its arsenal of nuclear weapons and the missiles to fire them across Asia and at the United States, the question of China's ability to rein in its old ally has taken on particular urgency.
