Makes one's case (6)
I believe the answer is:
argues
'makes one's case' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for argues that I've seen before include "Contends, debates" , "Disputes, expresses disagreement" , "Quarrels or disagrees" , "Debates or bickers" , "Disputes, proposes the contrary" .)