Judged to be a traitor to the editor (5)
I believe the answer is:
rated
'judged' is the definition.
(rating is a kind of judging)
'a traitor to the editor' is the wordplay.
'a traitor' becomes 'rat' (rat can mean a treacherous person).
'to the editor' becomes 'ed' (abbreviation).
'rat'+'ed'='RATED'
'to be' acts as a link.
(Other definitions for rated that I've seen before include "Assessed, valued" , "Censured" , "Classified or graded" , "Adjudged" , "Graded, ranked" .)