Real trouble after month in state (7)
I believe the answer is:
declare
'state' is the definition.
(declaring is a kind of stating)
'real trouble after month' is the wordplay.
'trouble' indicates an anagram.
'after' says to put letters next to each other.
'month' becomes 'dec' (abbreviation for December).
'real' with letters rearranged gives 'lare'.
'lare' after 'dec' is 'DECLARE'.
'in' is the link.
(Other definitions for declare that I've seen before include "say" , "Proclaim" , "Announce 13 closed" , "Profess" , "Announce formally" .)