At some point it was pointed out that George W. Bush DID have a higher IQ than John Kerry. As far as I know, this did not affect anyone's judgment of him in the slightest. The people who liked him still liked him. The people who thought he was an idiot still thought he was an idiot in the ways that actually mattered.
What I remember was that he had a higher college GPA...
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.