Failing to put pressure on inhabitant to become second-in-command (4,9)
I believe the answer is:
vice president
'second-in-command' is the definition.
(I know that vice-president is a type of second-in-command)
'failing to put pressure on inhabitant' is the wordplay.
'failing' becomes 'vice' (vice can mean a moral failing).
'to put' means one lot of letters go next to another.
'pressure' becomes 'p' (abbreviation).
'on inhabitant' becomes 'resident' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'vice'+'p'+'resident'='VICE-PRESIDENT'
'to become' is the link.
Can you help me to learn more?
(Other definitions for vice president that I've seen before include "US leader's deputy" , "Number two to 46, say" , "Second-in-command" , "senior politician" , "High-up executive officer" .)