Leave a politician after a month (6)
I believe the answer is:
decamp
'leave' is the definition.
(I know that decamp is a kind of leave)
'a politician after a month' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'after' says to put letters next to each other.
'a month' becomes 'Dec' (abbreviation for December).
'a'+'mp'='amp'
'amp' after 'dec' is 'DECAMP'.
(Other definitions for decamp that I've seen before include "Make off - from tent?" , "Go away suddenly or secretly - leaving tent?" , "Fold tents and go" , "Run away (unseen)" , "Fold up tent and depart" .)