I didn't know there was an official name for a political spoiler until today. You know, the candidate that is similar to another, more popular candidate of one of the major parties. Usually the spoiler only differs in a hand full of points from the main party candidates. In all cases, the spoiler is always, without exception, running for ego driven, self-aggrandizement purposes. Otherwise, they'd focus on getting their "team member" elected and work with the major candidate's administration to get their points of views worked on from within the system.
The bad thing (at least when it's your party) about the spoiler is that they drain away enough votes from their ideological peer to allow the opposition party to win. Think Ralph Nader's affect on Al Gore's chances for United States president in 2000.
Thanks to Anu Garg's Wordsmith.org A Word A Day email, now I know the official word for political spoiler.
Stalking Horse 1
1. Something used to mask the true purpose.
2. A candidate put forward in an election to draw votes from another or to conceal another's potential candidacy.
ETYMOLOGY: After the former practice of bird hunters of hiding behind a horse (or a decoy) until he had reached within close range of prey.
This week's theme: words about government, politics, and elections.
Stalking Horse 2
1. Something used to cover one's true purpose; a decoy.
2. A sham candidate put forward to conceal the candidacy of another or to divide the opposition.
3. A horse trained to conceal the hunter while stalking. A canvas screen made in the figure of a horse, used for similar concealment.