Douglas Harper's Etymology Dictionary
Wiktionary
a. (context of a person English) incapable of being elected to political office, especially due to a lack of suitable qualities or policies.
Usage examples of "unelectable".
Whereas in France the Communists had earned themselves a rightful and respected place in political life, the Greek Communists made themselves permanently unelectable because even Communists could not bring themselves to vote for them.
The opposition party, knowing it couldn't win anyway, had thrown a sop to the Old Left hardcases who were its shock troops by nominating one of their own: the patently unelectable Harvey Langston, congressman from a California district for which the term "La-La Land" might well have been coined.
Besides, the husband was as boring as a dead toad and unelectable in his own right.