Presidential candidate once sounded a bit wet (4)
I believe the answer is:
dewy
'a bit wet' is the definition.
'presidential candidate once sounded' is the wordplay.
'presidential candidate once' becomes 'dewey' (1948 US presidential candidate Thomas Dewey).
'sounded' shows a homophone (sound like).
'dewey' is a homophone of 'DEWY'.
(Other definitions for dewy that I've seen before include "Fresh early on" , "Wet with condensation" , "wet grass" , "laden with pearls" , "fresh in the morning?" .)