1. To denounce and reject a friend, mentor, relative, colleague, or casual acquaintance for the sake of political expediency.
2. Something that critics demand politicians do to the allegedly toxic people they are allegedly connected to. Only applies to black presidential candidates, who can throw their acquaintances under the bus repeatedly without ever satisfying the media's taste for roadkill.
January: Why doesn't Obama throw his former pastor, Rev. Jeremiah Wright, under the bus?
May: Why did Obama wait so long to throw Wright under the bus?
June: Who else will Obama need to throw under the bus?