Might have an obligation to reside in Puerto Rico (5)
I believe the answer is:
power
'might' is the definition.
(being mighty)
'have an obligation to reside in puerto rico' is the wordplay.
'have an obligation' becomes 'owe' (to owe someone is to have an obligation to them).
'to reside in' is an insertion indicator.
'puerto rico' becomes 'PR' (abbreviation for Puerto Rico).
'owe' put inside 'pr' is 'POWER'.
(Other definitions for power that I've seen before include "Supply with energy" , "Exponent" , "Electricity or strength" , "Physical force, ability" , "Military potential" .)