Influencer in hallway first (8)
I believe the answer is:
lobbyist
'influencer' is the definition.
(someone who lobbies politicians)
'hallway first' is the wordplay.
'hallway' becomes 'lobby' (I am not sure about this - if you are sure you should believe this answer much more).
'first' becomes 'ist' (ist resembles lst).
'lobby'+'ist'='LOBBYIST'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for lobbyist that I've seen before include "figure influencing lawmakers" , "'To - it may concern'" , "One tries to influence government in favour of their cause" , "One seeks to influence legislators" , "political campaigner" .)