noun
party member; party loyalist
Refers to a committed, often long-standing member of a political party, sometimes with a connotation of being deeply entrenched or unwavering in party loyalty.
彼は生粋の党人で、党の方針に絶対の信頼を置いている。
He is a dyed-in-the-wool party member, placing absolute trust in the party's policies.
党人たちは選挙戦に向けて結束を固めた。
The party members strengthened their unity for the election campaign.