What is Hatchet man (idiom)?

In the context of the Watergate scandal, the term hatchet man was used to refer to a trusted and particularly orthodox subordinate tasked by his employer with destroying a political opponent by any means necessary. Charles Colson was known as a hatchet man for President Richard Nixon, as was H.R. Haldeman, who proudly described himself as "Richard Nixon's 'son of a bitch'". This use of the term has since become commonplace for anyone who is tasked with conducting distasteful, illegal, or unfair "dirty work" to protect the reputation or power of their employer.