What does "dead duck" mean?

A person doomed to failure or death; a hopeless case. For example, If they can't find a heart to transplant soon, he's a dead duck. [1940s]

A useless, worthless, or outmoded person or thing. For example, They didn't interview the outgoing senator; to the press he's a dead duck. Some speculate that this slangy term comes from an old saying, “Never waste powder on a dead duck,” first recorded in 1829.