just because he and the candidate are both black

Right ...
... not because he's experienced, not because his military credentials are totally legitimate as compared to the republican who was riding bicycles in France when Powell wore his uniform, not because he's been closer to American foreign affairs than anyone on the republican's staff

... but just because he and the candidate are both black.

Using that logic, I could justifiably diminish and dismiss any old white guy with tons of credentials who has endorsed the republican

... just because they are both white. There would be no difference in such a dismissal in any way.