He ultimately avoided military service - 'Tool!' Democrat maintained (5,6)
I believe the answer is:
draft dodger
'he ultimately avoided military' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'service tool democrat maintained' is the wordplay.
I cannot quite understand how this works, but
'service' could be 'raf' (Royal Air Force) and 'raf' is present in the answer.
'democrat' could be 'd' and 'd' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for draft dodger that I've seen before include "Reluctant GI" , "One avoiding conscription (US)" .)