support base; power base
Political term referring to the foundation of support, especially in an electorate or organization.
The politician frequently returned to his hometown to solidify his local support base.
The party's support base is weakening.
支持基盤 is a general term for any kind of support base (political or otherwise), whereas 票田 specifically refers to a region or group that supplies votes.
Compound of 支持 (support) and 基盤 (base, foundation).