When President Xi Jinping of China took power almost five years ago, he quickly gained control of the commanding heights of the Chinese party-state, taking charge of the military, foreign policy, domestic security and a fearsome anticorruption commission.

In centralizing decision making in his office, Mr. Xi also grabbed hold of something his two immediate predecessors never did during their lengthy stays in office: He placed himself in charge of economic policy.

Mr. Xi’s authoritarian instincts have served him well politically. Chinese leaders from Mao Zedong onward have always had rivals among senior leaders. As he looks ahead to securing a second five-year term at the Communist Party Congress in the fall, Mr. Xi appears to have none.

With this enormous power, Mr. Xi has pushed through once-in-a-generation changes in military structure and personnel, built a new national security council, pressed China’s claims in the South China Sea and overseen the largest antigraft campaign since the 1949 Communist Revolution.