Failure may be slander, with daughter in for leader (3)
I believe the answer is:
dud
'failure' is the definition.
(dud is a kind of failure)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for dud that I've seen before include "Ineffectual thing/person" , "Failing in its function" , "Palindrome for a flop" , "Firework not going up" , "Phoney" .)