Trump, scratching bottom, is a terrible fellow (4)
I believe the answer is:
ivan
'a terrible fellow' is the definition.
(Russian tsar Ivan the Terrible)
'trump scratching bottom' is the wordplay.
'trump' becomes 'Ivana' (Ivana Trump, Donald ex wife).
'scratching bottom' means to remove the last letter.
'ivana' with its final letter removed is 'IVAN'.
'is' is the link.
(Other definitions for ivan that I've seen before include "One Day in the Life of - Denisovich (Solzhenitsyn)" , "in Russian history" , "Tsar - 197> the Terrible" , "A Russian emperor, quite Terrible" , "Russian tsar called 'the Terrible'" .)