Conservative departing America's heart to submit (5)
I believe the answer is:
enter
'to submit' is the definition.
(as in to submit something to a competition)
'conservative departing america's heart' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'departing' is a deletion indicator.
'america's heart' becomes 'center' (US spelling of 'centre').
'center' with 'c' taken away is 'ENTER'.
(Other definitions for enter that I've seen before include "Go in and put in the ledger" , "Pierce" , "Enlist, join up" , "cross the threshold" , "Come in - register" .)