BEIJING—One morning in mid-January, about 120 of the Communist Party’s top disciplinarians gathered to hear Chinese President Xi Jinping chart their priorities for the new year. After a three-year anticorruption sweep in which some 750,000 party members were punished, Mr. Xi now had another demand: enforce unswerving loyalty to preserve “the party’s centralized unity.”

A number of officials were penalized in recent months for internal dissent—described as political deviance—while Mr. Xi called on cadres, academics and journalists...