What the candidate must do before winning a seat (5)
I believe the answer is:
stand
This clue might be a double definition.
'what the candidate must do before winning a' is the first definition.
The definition suggests a singular noun which matches the answer.
'seat' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for stand that I've seen before include "remain in force" , "Be likely to rise" , "Set up" , "Decline to interfere when one should?" , "Base < put up with" .)