Leader potentially real idiot (9)
I believe the answer is:
editorial
'leader' is the definition.
(type of newspaper article)
'potentially real idiot' is the wordplay.
'potentially' is an anagram indicator (letters have the potential to spell a new word).
'real'+'idiot'='realidiot'
'realidiot' is an anagram of 'EDITORIAL'.
(Other definitions for editorial that I've seen before include "paper item" , "Newspaper opinion piece" , "Article written" , "Article giving a newspaper's opinion" , "Article expressing the views of the publication" .)