Reluctant promise to support Liberal (5)
I believe the answer is:
loath
'reluctant' is the definition.
('loath' can be a synonym of 'reluctant')
'promise to support liberal' is the wordplay.
'promise' becomes 'oath' (I've seen this before).
'to support' says to put letters next to each other (in a down clue, some letters hold others up).
'liberal' becomes 'l' (abbreviation).
'oath' after 'l' is 'LOATH'.
(Other definitions for loath that I've seen before include "Hateful" , "Reluctant or averse" , "Dislike intensely" , "Unwilling" .)