thrown under the bus

To sacrifice someone, typically one who is undeserving, in order to make political gain.

Newsweek: “In general, ‘thrown under the bus’ is a metaphor for what happens when someone takes a hit for someone else’s actions. But unlike its etymological cousins, ‘scapegoat’ and ‘fall guy,’ the phrase suggests a degree of intimacy between the blamer and the blamed.”

Word Detective: “I think the key to the phrase really lies in the element of utter betrayal, the sudden, brutal sacrifice of a stalwart and loyal teammate for a temporary and often minor advantage.”