Attack one politician with a plastic gun (6)
I believe the answer is:
impugn
'attack' is the definition.
(thesaurus)
'one politician with a plastic gun' is the wordplay.
'one politician' becomes 'imp' (I've seen this in other clues**).
'with' says to put letters next to each other.
'a plastic' indicates anagramming the letters (plastic can mean easily moulded).
'gun' is an anagram of 'ugn'.
'imp'+'ugn'='IMPUGN'
(Other definitions for impugn that I've seen before include "Dispute the truth of" , "Try to discredit, express doubts about honesty" , "Express doubts about truth or honesty of, say motives" , "Call into question or attack by words" , "Dispute honesty of (someone's motive)" .)