Quick to remain in office (6)
I believe the answer is:
presto
'quick' is the definition.
(I've seen this before)
'remain in office' is the wordplay.
'remain' becomes 'rest' (synonyms).
'in' means one lot of letters goes inside another.
'office' becomes 'po' (I am not sure about this - if you are sure you should believe this answer much more).
'rest' inserted inside 'po' is 'PRESTO'.
'to' is the link.
Can you help me to learn more?
(Other definitions for presto that I've seen before include "quickly in bars" , "Hey . . . . ., says the magician (6)" , "In a quick tempo (music)" , "To be played quickly" , "Hey ..., said the magician" .)