• 政党せいとう — political party
• 与党よとう — ruling party
• 野党やとう — opposition party
• 党首とうしゅ — party leader
• 悪党あくとう — villain; rogue

党 originally referred to a group of people with shared ancestry or goals. Over time, it came to represent political groups, factions, and cliques. The 儿 (legs) radical may suggest movement or people. In modern Japanese, it is almost always connected to politics and organizations.

彼かれは 与党よとうの 党首とうしゅです。
He is the leader of the ruling party.

二大にだい政党せいとうが 争あらそっています。
The two major political parties are in conflict.