Challenge intended to undermine Democrat leader in election (8)
I believe the answer is:
defiance
'challenge' is the definition.
(I know that defiance is a type of challenge)
'intended to undermine democrat leader in election' is the wordplay.
'intended' becomes 'fiance' (who someone intends to marry).
'to undermine' says to put letters next to each other (in a down clue, some letters go under others).
'democrat' becomes 'd'.
'leader in' indicates taking the first letters.
The initial letter of 'election' is 'e'.
'd'+'e'='de'
'fiance' after 'de' is 'DEFIANCE'.
(Other definitions for defiance that I've seen before include "Refusal to obey" , "Bold disobedience" , "to make a challenge" , "Resistance to authority" , "Refusal to comply" .)