Well, what do you mean by "authentic"? I don't care for nationalist essentialism, so in that sense of "real" or "not real", of course every American is as authentic as every other. And they all have the right to have their voices heard.

But if by "authentic" you mean working towards, rather than against, an America that is as great, free and egalitarian as it should be, and as it likes to consider itself, then never mind black or non-black: The liberal or, by American standards, the left-radical America is the only authentic America, full stop.