Leader breaking up ideal trio (9)
I believe the answer is:
editorial
'leader' is the definition.
(I've seen this before)
'breaking up ideal trio' is the wordplay.
'breaking up' indicates an anagram.
'ideal'+'trio'='idealtrio'
'idealtrio' anagrammed gives 'EDITORIAL'.
(Other definitions for editorial that I've seen before include "Statement of a newspaper's opinion" , "Article that states a newspaper's opinion" , "Article giving a newspaper's opinion" , "(Paper's) leader" , "bit of paper" .)