Last week, Chinese President Xi Jinping’s chief of staff Cai Qi, the fifth most senior official in the ruling Communist Party, was chosen to lead the Central Party School, Beijing’s leading academy for cadres. The Central Party School is not just any training site for Chinese officials, but part of a nationwide system that Xi considers key to the ideological purity of the party and important for the expertise needed by senior officials across the country. Who were previous heads? In the past...