In 686, fearful of the general Li Xiaoyi (李孝逸) -- a member of the imperial Li clan who had defeated the anti-Empress Dowager Wu rebellion led by Li Jingye the Duke of Ying in 684-Wu Chengsi made false accusations against him, and in response, Empress Dowager Wu demoted Li Xiaoyi.
In 689, Empress Dowager made Wu Chengsi Nayan (納言) -- the head of examination bureau of government and a post considered one for a chancellor.