Regret abusive Democrat must be removed (3)
I believe the answer is:
rue
'regret' is the definition.
(to rue something is to regret it)
'abusive democrat must be removed' is the wordplay.
'abusive' becomes 'rude' (rude can mean abusive or insulting).
'democrat' becomes 'd'.
'must be removed' is a deletion indicator.
'rude' with 'd' removed is 'RUE'.
(Other definitions for rue that I've seen before include "The 'herb of grace'" , "Bemoan" , "Lament; a herb" , "Be regretful" , "At one time, pity" .)