One US President, bad vote-loser (9)
I believe the answer is:
roosevelt
'one us president' is the definition.
(Theodore Roosevelt or Franklin Delano Roosevelt)
'bad vote-loser' is the wordplay.
'bad' is an anagram indicator.
'vote'+'loser'='voteloser'
'voteloser' with letters rearranged gives 'ROOSEVELT'.
(Other definitions for roosevelt that I've seen before include "Surname of 26th and 32nd US presidents" , "former president" , "Leading statesman in war" , "One of two US presidents" , "Long-term leader" .)