Missouri House Republicans were told they could face primary opposition this year if they voted to sustain Governor Jay Nixon's veto of income tax cut legislation.
Fifteen Republicans voted anyway against the override despite the threats, but only four drew primary challengers for this year's election as candidate filing closed this past week.
The Missouri Club for Growth, which promised to recruit primary challengers, said they have spoken to those challengers. But the group declined to say if it would provide financial backing to those campaigns.
The link between the tax vote and Republican primaries isn't clear. A political scientist from Missouri State University said many of the incumbents would have drawn challengers regardless of their vote.