mad dog

In Canadian politics as usual a mad dog is an independent or minor party candidate who is nominally an electoral rival for the same post, but in fact is focused on disabling someone else's candidacy, not getting elected himself or herself. The mad dog systematically devotes energy to negative campaigning against a particular candidate, to ensure that candidate cannot stay on-message but must devote time to responding to this.

By contrast a wingman props up a friendly candidate, and will always publicly detest and deny that they have any role in helping the mad dog develop their campaign tactics. In fact, however, mad dogs and wingmen are often used in coordination to ensure the "right" candidate wins.

Whole parties can be considered to be mad dogs at times, e.g. the Family Heritage Party is often so-called.