Liberal MP is bad — without question, a disappointment. (4,5)
I believe the answer is:
damp squib
'a disappointment' is the definition.
(a damp squib is something underwhelming)
'liberal mp is bad without question' is the wordplay.
'liberal' indicates anagramming the letters.
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'question' becomes 'qu'.
'mp'+'is'+'bad'='mpisbad'
'mpisbad' anagrammed gives 'dampsib'.
'dampsib' placed around 'qu' is 'DAMP SQUIB'.
(Other definitions for damp squib that I've seen before include "set up by a guy?" , "Unsuccessful attempt to impress - firework won't ignite?" , "Something that fails to have the expected impact" , "Unsuccessful attempt to impress with moist explosive" , "Let-down" .)