Deserter from the Democratic Party (3)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
rat
'deserter' is the definition.
(thesaurus)
'from the democratic party' is the wordplay.
'from' says the answer is hidden in the clue.
'RAT' is hidden in the letters of 'democratic party'.
(Other definitions for rat that I've seen before include "Destructive rodent" , "Rodent pest" , "Unpleasant character" , "Scumbag" , "Cad" .)