I'm undecided on that because that increasing racism by Republicans towards Obama coincided with the period when both Democracts and Republicans moved more and more of their political propaganda into the domain of Identitarian Wars: whilst before there was still a lot of talk about Economics, later the loud shouting was all about people's race, country of birth, religion, gender and sexual orientation.

It's unclear if the increase of the racism from the Republicans towards Obama was directly due to Obama's being a black POTUS or if it was a reflection of a wider trend: it's just as logical an explanation that with the 2008 Crash and both parties being unified in shoving money to Financial Institutions and saving large Asset Owners at a significant cost (i.e. Austerity) for the rest of Society, they had to switch their discourse from Economics (were their actions in the post-2008 Crash had made painfully clear there was no significant difference between both) and into the Moral space, which from the side of the Republicans means amongst other things turning up the racist speech, with Obama being the most visible minority-member recipient of it.