Not standing as a politician, many would assume? (5)
I believe the answer is:
lying
This clue is a double definition.
'not standing' is the first definition.
('lie' is the opposite to 'stand')
'as a politician many would assume?' is the second definition.
(politicians frequently lie)
(Other definitions for lying that I've seen before include "Deceit" , "Spread out" , "Fabrication" , "Anything but upright" , "Prostrate -- prone" .)