If, hypothetically, Sarah Palin was identified as having genes that made it 70% likely that she was a sociopath, it would get reported by CNN. Bill O'Reilly would yell about how it's easy to tell that Sarah Palin is not a sociopath if you actually spend five minutes with her, rather than getting all your information filtered by the liberal media. Liberal groups would yell about how this confirmed all of their suspicions that Sarah Palin was a lying manipulator. Conservative tea partiers would make comments about "liberal evolutionist scientists" trying to discredit an American hero. More contemplative conservatives would point to this as an example of an innocent woman being discriminated against by immoral technologies, built by scientists who were "playing god".
I originally wrote Barack Obama, but many liberals are frustrated with him, so I decided to write the scenario with a more polarizing figure. The point is, no matter how serious of well backed up the science is, there is no situation I can think of where political instincts wouldn't be able to reduce the reasoning abilities of the average voter down to the level of a chimpanzee in a poo-fight.
If this sort of genetic testing existed, then politicians with very bad genes would never make it through the presidential primaries; they'd be filtered out before it got to partisans spinning or ignoring the evidence.
I wrote an article for h+ predicting that the rapid fall in the cost of gene sequencing will allow U.S. voters to learn much about presidential candidates' DNA. The candidates won't be able to stop this because:
DNA analysis has a decent chance of reducing political bias by providing objective information about candidates. If, for example, 70% of the variation in human intelligence is determined by identified genes then DNA analysis would reduce disagreements among informed voters over a candidate's intelligence.