Just think Bush at 43% was after years of liberal media bashing. In contrast to Obama's literal sycophant lapdog media, he gets a 40% that's really a Affirmative Action bump. If he was treated like Bush was, he would be in the 20% range and that's a fact.
Presidential Job Approval Center
In fairness, Bush was white and this country still has many pockets of racism and bigotry.
Take out the people who can't see past the color of Obama's skin and I'd put him at 55%.
Dig a little deeper and pull out the closet racists -- those less overt folks screaming about college transcripts and Marxism -- and I'd put him at 65%.
But this means, also in fairness, that if you eliminated those prejudiced against Bush because of the color of his skin -- then he'd be at about 47%.