Chen Xitong
On July 24, 2017, the Central Commission for Discipline Inspection announced that Sun was undergoing investigation for violating party discipline. The announcement marked the first time that a sitting Politburo member was investigated by the CCDI since Xi Jinping assumed power as General Secretary of the Communist Party of China at the 18th Party Congress. Before Sun, the last incumbent Politburo member subject to investigation was Bo Xilai (also then serving as Chongqing party secretary) in April 2012. Sun was the fourth sitting Politburo member investigated after 1990 - following Chen Xitong, Chen Liangyu, and Bo Xilai; all of them were party chiefs of direct-controlled municipalities.