Ruling party on the left, around south, is supported uncommonly (8)

'supported uncommonly' is the definition.
'indorsed' can be an answer for 'supported' (indorsing is a kind of supporting). I'm not certain of the 'uncommonly' bit.

'ruling party on the left around south' is the wordplay.
'ruling' becomes 'in' (the ruling party is voted 'in').
'party' becomes 'do' (do is a kind of party).
'on the left' becomes 'red' (I can't explain this - if you can you should believe this answer much more).
'around' indicates putting letters inside.
'south' becomes 'S' (synonyms).
'red' enclosing 's' is 'rsed'.
'in'+'do'+'rsed'='INDORSED'

'is' acts as a link.

Can you help me to learn more?