Definition of Dark Horse Candidate
In the world of politics, a "dark horse candidate" is a person who is unheralded but becomes unexpectedly successful over the course of a campaign.
At the beginning of a campaign, a "dark horse candidate", by definition, is not known to the masses. The dark horse candidate has some supporters, but they are generally overlooked by the majority of the population who are drawn to other candidates.

This is the definition of a "dark horse candidate" - somebody who was unheralded at the start of a campaign that ends up achieving an unexpected level of success.
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