To do with politician stopping as he is suffering too much stress (12)
I believe the answer is:
overemphasis
'too much stress' is the definition.
(I've seen this before)
'to do with politician stopping as he is suffering' is the wordplay.
'to do with' becomes 'over' (both can mean relating to or as a result of).
'politician' becomes 'mp' (Member of Parliament).
'stopping' means one lot of letters goes inside another (stopping can mean blocking a gap).
'suffering' is an anagram indicator.
'as'+'he'+'is'='asheis'
'asheis' is an anagram of 'ehasis'.
'mp' going into 'ehasis' is 'emphasis'.
'over'+'emphasis'='OVEREMPHASIS'
(Other definitions for overemphasis that I've seen before include "Excessive underlining" , "Excessive stress" , "Too much stress" .)