power base
noun [ C usually singular ] uk/ˈpaʊə ˌbeɪs/ us/ˈpaʊ.ɚ ˌbeɪs/
（某人的）后盾，权力基础
an area of a country or a group of people on which someone's power depends
The industrial cities are the Labour Party's traditional power base. 工业城市是工党传统的权力基础所在。