Entrenched Republican suggested removing leader (6)
I believe the answer is:
rooted
'entrenched' is the definition.
(I've seen this in another clue)
'republican suggested removing leader' is the wordplay.
'republican' becomes 'ro' (I can't explain this - if you can you should give a lot more credence to this answer).
'suggested' becomes 'voted' (I've seen this before).
'removing leader' means to remove the first letter.
'voted' with its first letter removed is 'oted'.
'ro'+'oted'='ROOTED'
Can you help me to learn more?
(Other definitions for rooted that I've seen before include "Firmly established in a plantlike way" , "Fixed in place like plants in soil" , "Stuck to the spot" , "Firmly established and well planted" , "(Of new cutting) firmly established" .)