Nguyen Phu Trong has emerged as an unlikely strongman. Widely regarded as a compromise figure when he became Vietnam's general secretary in 2011, the 74-year-old ideological hard-liner has quickly reshaped the balance of Vietnam politics since assuming the post of Communist Party chief. On Oct. 22, Vietnam's parliament will formally approve Trong's presidency, effectively breaking his long-espoused model of collective leadership to become the most powerful Vietnamese leader in recent decades. But unlike Chinese President Xi Jinping, Trong is far from a supreme leader; his advanced age almost certainly guarantees his retirement at the next party congress in 2021 -- a factor that also raises questions about his plan for succession and the sustainability of a more individualistic rule in what remains a factional political scene. For the moment, however, maintaining a mere grip on power is only half of Trong's task. Beyond that, Vietnam's leader will strive to mobilize...