Almost all actors put up with Republican bully that can't be criticised (6,3)
I believe the answer is:
sacred cow
'can't be criticised' is the definition.
I can't judge whether this defines the answer.
'almost all actors put up with republican bully' is the wordplay.
'almost all' means to remove the last letter (most but not all of the word).
'actors' becomes 'cast' (group of actors).
'put up' shows that the letters should be reversed in order.
'with republican' becomes 'red' (traditional colour for US republican party. I am not sure about the 'with' bit.).
'bully' becomes 'cow' (cow can mean to bully or oppress).
'cast' with its final letter taken away is 'cas'.
'cas' back-to-front is 'sac'.
'sac'+'red'+'cow'='SACRED COW'
'that' acts as a link.
Can you help me to learn more?
(Other definitions for sacred cow that I've seen before include "Object beyond criticism" , "Something bovine above criticism?" , "Institution not to be criticised" , "Person, custom, etc unreasonably held to be beyond criticism" , "One immune to criticism" .)