Republican with no real intelligence rebuffed left-wing attacker (6)
I believe the answer is:
raider
'attacker' is the definition.
(I've seen this before)
'republican with no real intelligence rebuffed left-wing' is the wordplay.
'republican with no real intelligence' becomes 'rai' (I can't justify this - if you can you should believe this answer much more).
'rebuffed' is a reversal indicator.
'left wing' becomes 'red' (red can informally mean communist).
'red' in reverse letter order is 'der'.
'rai'+'der'='RAIDER'
Can you help me to learn more?
(Other definitions for raider that I've seen before include "Viking" , "Armed insurgent" , "person taking food from larder" , "Pillager, plunderer" , "One who makes a sudden swift attack" .)