Gosh — close to Biden securing victory! (2,4)
I believe the answer is:
by jove
'gosh' is the definition.
(both are expressions of surprise)
'close to biden securing victory' is the wordplay.
'close' becomes 'by' (I've seen this in other clues).
'to biden' becomes 'joe' (Joe Biden).
'securing' is an insertion indicator.
'victory' becomes 'v'.
'joe' going around 'v' is 'jove'.
'by'+'jove'='BY JOVE'
(Other definitions for by jove that I've seen before include "Good God!" , "Crikey!" , "Surprised exclamation" , "Well, I'm blowed!" , "Old exclamation of surprise invoking Jupiter" .)