Vital element of libel squandered before party withdraws (9)
I believe the answer is:
lifeblood
'vital element' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for lifeblood that I've seen before include "Factor indispensable for strength and vitality" , "The vital factor" , "essential factor" .)