Niu Sengru
In 832, during the reign of Emperor Jingzong's younger brother Emperor Wenzong, Du Cong was made the mayor of Jingzhao Municipality (京兆, i.e., the region of the Tang capital Chang'an). At that time, he was considered a close associate of the chancellor Li Zongmin, a leader of the faction later known as the Niu Faction (named after Li Zongmin's ally Niu Sengru) in the Niu-Li Factional Struggles. He tried to broker a peace between Li Zongmin and Li Deyu, a leader of the rival Li Faction (after whom the Li Faction was named), by suggesting that Li Zongmin offer to recommend Li Deyu to oversee the imperial examinations. Li Zongmin rejected the idea, but agreed to Du's alternate proposal of recommending Li Deyu as chief imperial censor; Li Deyu was pleased, but when Li Zongmin subsequently reneged, the possibility of peace between Li Zongmin and Li Deyu was broken.