1
general::
Phrase(s): back the wrong horse
Fig. to support someone or something that cannot win or succeed. • I don’t want to back the wrong horse, but it seems to me that Jed is the better candidate. • Fred backed the wrong horse in the budget hearings.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, bet on the wrong horse. Guess wrongly or misjudge a future outcome, as in Jones garnered only a few hundred votes; we obviously backed the wrong horse, or Counting on the price of IBM to rise sharply was betting on the wrong horse. Transferred from wagering money on a horse that fails to win the race, a usage dating from the late 1600s, this term is widely applied to elections and other situations of uncertain outcome.
American Heritage Idioms