back the wrong horse

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.