Several years later I met George in New York while he was in the middle of his dark horse tour.
Today, though, the primary system makes it harder for a dark horse to make a splash.
Many conservatives are actively trolling for a dark horse to come in and rescue them from the current stable of 2012 candidates.
in politics, 1842, an image from horse racing, in which dark is used in its figurative sense of "unknown."
Moonraker is called a "dark horse"; that is neither his sire nor dam is known. ["Pierce Egan's Book of Sports," London, 1832]
An unexpected winner. In politics, a dark horse is a candidate for office considered unlikely to receive his or her party's nomination, but who might be nominated if party leaders cannot agree on a better candidate.
: a dark-horse candidate/ dark-horse oddsnoun phrase
A person or team, esp in sports or politics, that seems very unlikely to win but might nevertheless do so (1842+ fr horse racing)