I've told this story on this forum before, but Ima gonna do it again...
About five years ago a white male local democrat politician was in my shop at the same time a well known black business owner democrat lady was. He chatted with her about Obama for a minute, giving him praise. As soon as the lady left, he looked at me and said "how we gonna get that nigger out of office". I was floored at not only the racism, but also the hypocrisy.
I've heard several people refer to Obama as "that half black president", and doing it a very distinct tone of disgust in their voice.
Every president has haters, but never in my lifetime have I seen this degree of hatred directed towards any president. I highly suspect that racism, is one of the main factors, but I think there are some other factors going on.
One is the Great Bush Recession. Bush left our economy in shambles, and republicans have an intense fear that Obama is going to leave office with a booming economy. They don't want that to happen.
Some, like Rush, have openly said that they want our economy to fail - just to prove that Obama and/or liberal policies don't work.
These radical right wing extremists would rather the US fail, than to admit that conservative rhetoric isn't perfect and that liberal rhetoric isn't all bad.
A successful Obama administration is an embarrassment to both racists, and those on the extreme right.