Powell has proclaimed that, whatever his professed ideology, when it comes down to it his first loyalty is to a fellow black. He is not the first black "conservative" to make this move.
This will be noted by many whites who were thinking of voting for a black man under the assumption that he would be acting for the benefit of all the people he represented, rather than just those who "look like him". This move will be highly damaging for black conservatives everywhere.
Maybe Clarence Thomas, he can't be fired for his views and they have already cost him heavily in his community.