OK, I will put my biases on display as an example of why the kind of thing you're talking about doesn't work. My political views are generally opposed to Sarah Palin's in the context of US politics. If you told me that, despite the judgments I formed listening to her talk in public, there is genetic evidence that she is actually very smart and Joe Biden is very stupid, I would reply "Then I feel sorry for the good Lord. She sounded like a world-class idiot." I think most people, mutatis mutandis, would respond similarly.
In other words, I doubt that our confidence in DNA evidence regarding things like intelligence (which, NB, is surely correlated only imperfectly with skill in governing, which is one of the points I was trying to make in my comment below), is going to trump things like political ideology and our own judgments of whether someone sounds smart or not when they talk.
Er, Biden's pretty stupid. Palin's pretty stupid too, but I only suspect Biden's IQ is higher with about 60% confidence.
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.