Take in upsetting barbs about opposition leader (6)
I believe the answer is:
absorb
'take in' is the definition.
(synonyms)
'upsetting barbs about opposition leader' is the wordplay.
'upsetting' is an anagram indicator.
'about' indicates putting letters inside.
'leader' indicates taking the first letters.
The first letter of 'opposition' is 'o'.
'barbs' is an anagram of 'absrb'.
'absrb' enclosing 'o' is 'ABSORB'.
(Other definitions for absorb that I've seen before include "Take or drink in" , "Occupy the mind fully as good book will" , "Take in and digest, food or knowledge" , "Assimilate, integrate" , "Grip" .)