Promised to employ Democrat (7)
I believe the answer is:
engaged
'promised' is the definition.
('engaged' can be a synonym of 'promised')
'employ democrat' is the wordplay.
'employ' becomes 'engage' (engaging is a kind of employing).
'democrat' becomes 'd'.
'engage'+'d'='ENGAGED'
'to' is the link.
(Other definitions for engaged that I've seen before include "Taken on - betrothed" , "Employed - to be married? (7)" , "Fully occupied" , "Given a ring" , "preparing for the match?" .)