throw sb under the bus

throw sb under the bus (to sacrifice someone to gain an advantage; to treat as a scapegoat; to put out of favor or at a disadvantage) — принести кого-л. в жертву (в угоду своим интересам, выгоде); предать, сдать; ≅ кинуть

Example 1: He wants a promotion so bad, he’ll throw anyone under the bus to get it. (ebaby)

Example 2: I can’t believe you’re going to throw me under the bus after all I’ve done for you. (ebaby)

Example 3:
Question: You looked shocked when Steve took the stand. Why?
Anderson Cooper: Basically because he had — he had changed his entire — his testimony. He just — he just lied. I — I just can't believe the way he portrayed me and the way he just threw me under the bus to protect himself.
(LAUREN O'DELL GOES ON TRIAL FOR THE MURDER OF EVAN HIPPEARD, 1998)

Example 4: It seems like every campaign every day has had to throw somebody under the bus. And Senator Gramm yesterday got thrown — it was his turn to go under the bus.

Exactly who is throwing whom and from where did this much-abused phrase come? Is it time to throw 'under the bus' under the bus?