China needs a strong leader like President Xi Jinping. Only an assertive head of state could reset the ineffective bureaucracy and put the country on a path toward meaningful reform. But like many strongmen, Mr. Xi appears to be reaching too far.

Since the 1980s, the Communist Party has followed an unwritten rule to ensure an orderly leadership transition and prevent a Mao-style autocracy. The head of the party serves a 10-year term and, halfway into his tenure, he nominates a successor with the help of party elders. In Mr. Xi’s case, he would need to name an heir at the party convention next year.

In previous cycles, by this time in a party leader’s tenure, names of potential successors would have already emerged. But there has been no public discussion or leaked names. While it’s possible that Mr. Xi is taking more time to pick an heir, there are indications that he intends to break with custom and hold on to his role as head of the party beyond the 10-year term. (“President” is a ceremonial title; the Communist Party general secretary wields the real power.)

In recent months, Mr. Xi has promoted many allies in key government and party positions to fill slots vacated by retired or purged rivals. He has been overhauling the military, making it more difficult for generals to disobey or to stage a coup. Neither Mao Zedong nor Deng Xiaoping was able to achieve such control.