Fellow politician in US city first to gripe (8)
I believe the answer is:
complain
'gripe' is the definition.
(thesaurus)
'fellow politician in us city first' is the wordplay.
'fellow' becomes 'co' (I've seen this in other clues).
'politician' becomes 'mp' (Member of Parliament).
'us city' becomes 'LA'.
'first' is a charade indicator (letters next to each other).
'in' after 'la' is 'lain'.
'co'+'mp'+'lain'='COMPLAIN'
'to' acts as a link.
(Other definitions for complain that I've seen before include "Lament" , "Find fault" , "Grumble, carp" , "Bellyache" , "Grouse, grumble" .)