shoo-in

verb phrase

To cause a particular horse, esp an inferior one, to win a race

[1908+ Horse racing; fr the notion that the beast, not caring to run and not needing to, can be shooed over the finish line and win]

modifier

: to be a shoe-in candidate

noun

1. A horse that wins a race by prearrangement (1928+ Horse racing)
2. A person, team, candidate, etc, certain to win; cinch, sure thing: The big, powerful Trojans were the shoo-ins (1939+)

[shoe-in may simply be a misspelling, but it is probably based on a misunderstanding of the origin of the term; it is a sort of folk etymology]