Perhaps pretentious political group out of power (4)
I believe the answer is:
arty
'perhaps pretentious' is the definition.
'political group out of power' is the wordplay.
'political group' becomes 'party' (a political party).
'out of' suggests deleting specific letters.
'power' becomes 'p' (symbol in physics).
'party' with 'p' taken out is 'ARTY'.
(Other definitions for arty that I've seen before include "Boho" , "Affectedly artistic" , "Affectedly cultured" , "aesthetic pretensions" , "Affectedly unconventional" .)