Reach agreement, Republican having withdrawn (7)
I believe the answer is:
contact
'reach' is the definition.
(I know that reach can be written as contact)
'agreement republican having withdrawn' is the wordplay.
'agreement' becomes 'contract' (contract is a kind of agreement).
'republican' becomes 'r' (abbreviation).
'having withdrawn' indicates named letters should be taken away.
'contract' with 'r' removed is 'CONTACT'.
(Other definitions for contact that I've seen before include "Juxtaposition" , "Meeting" , "Connection" , "Useful acquaintance" , "Touching" .)