also: ふたまたごうやく
double-dealer; timeserver; fence-sitter
Refers to a person who opportunistically switches allegiance between two opposing sides for personal gain. Often used in political or business contexts. The image is of a plaster (膏薬) that can stick to either leg (二股).
He is a double-dealing politician.
That guy is a timeserver, trying to stay in good with both factions.