“Trump possibly is a scoundrel,” Republican admitted (4)
I believe the answer is:
card
'trump possibly' is the definition.
(trump is a kind of card)
'scoundrel republican admitted' is the wordplay.
'scoundrel' becomes 'cad' (cad is a kind of scoundrel).
'republican' becomes 'R' (abbreviation in US politics).
'admitted' means one lot of letters goes inside another (inserted letters are admitted in).
'cad' enclosing 'r' is 'CARD'.
'is a' acts as a link.
(Other definitions for card that I've seen before include "Stiff paper; plastic money" , "one in a suit" , "appears in a suit" , "programme at race meeting" , "What may be used for greeting" .)