"I mean, you got the first mainstream African American who is articulate and bright and clean and a nice-looking guy."

Again, its the intention.

Obama - the first mainstream (as opposed to a minister of the church?) African American running for president

He is articulate and bright.

He's clean-cut and nice-looking or he's 'untarnished by political scandal' and good looking.

Seems to me Biden should think more carefully before speaking but did he intend it to be a slur? I don't think so.