The number for whites is the key to his re-electability. He got 43% of the white vote in 2008. 39% puts him in the danger zone. If he’s in the low 30’s in 2012, he’s toast.
According to the Gallup poll, Obama isn’t supported by 39% of non-Hispanic white voters, he’s supported by 39% of non-Hispanic white *adults*. If elections were held today, and approval rating was a perfect predictor of how people would vote, Obama would get maybe 1/3 of the non-Hispanic white vote. Obama is well into unectability turf.