Deadlock that is about fool supporting MP (7)
I believe the answer is:
impasse
'deadlock' is the definition.
('impasse' can be a synonym of 'deadlock')
'that is about fool supporting mp' is the wordplay.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'about' means one lot of letters goes inside another.
'fool' becomes 'ass' (ass is a kind of fool**).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'ass' after 'mp' is 'mpass'.
'ie' placed around 'mpass' is 'IMPASSE'.
(Other definitions for impasse that I've seen before include "Lack of movement" , "Standstill" , "deadlock results" , "Stalemate situation" , "cul-de-sac" .)