One arguing with Republican protester? Not the first (12)

I believe the answer is:

remonstrator

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'one arguing' is the definition.
The definition suggests a singular noun which matches the answer.

'republican protester? not the first' is the wordplay.
'republican' becomes 'R' (political abbreviation).
'protester?' becomes 'demonstrator' ('demonstrator' can be a synonym of 'protester').
'not the first' means to remove the first letter.
'demonstrator' with its initial letter taken away is 'emonstrator'.
'r'+'emonstrator'='REMONSTRATOR'

'with' is the link.

Can you help me to learn more?

(Another definition for remonstrator that I've seen is " I complain".)

I've seen this clue in The Times.

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