Mistake in party politics (4)
I believe the answer is:
typo
'mistake' is the definition.
(typo is a kind of mistake)
'in party politics' is the wordplay.
'in' indicates a hidden word.
'TYPO' is hidden within 'party politics'.
(Other definitions for typo that I've seen before include "Finger problem" , "literal, perhaps" , "Printer's error" , "Small printing error" , "Printing error (colloq.)" .)