Protest march about deserter with US politician (8)

I believe the answer is:

democrat

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'us politician' is the definition.
(I've seen this before)

'protest march about deserter' is the wordplay.
'protest march' becomes 'demo' (I can't explain this - if you can you should believe this answer much more).
'about' becomes 'c' (circa).
'deserter' becomes 'rat' (both can mean a traitor).
'demo'+'c'+'rat'='DEMOCRAT'

'with' acts as a link.

Can you help me to learn more?

(Other definitions for democrat that I've seen before include "US politician" , "Clinton or Obama supporter" , "American politician" , "Member of US political party" , "Believer in government of, for and by the people" .)

I've seen this clue in The Daily Express.

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