If there is a backlash against Beta, (and that remains to be seen), I don’t think his whiteness or sex is the source of it. After all, both Bernie Sanders and Joe Biden are white and male and I doubt in either case you’ll hear anything close to a similar form of criticism.
I think this may go a little deeper than that. Both political parties have their messiahs, for lack of a better term: the yearning for the candidate which they romantically associate with the “good old days”. For Republicans, at least until 2016, that guy has always been Ronald Reagan: they have sought someone who can be the “next Reagan”. For Democrats, it goes back even further: their glory figure was John F. Kennedy: young, charismatic, with golden dreams. Perhaps now its Barack Obama, who possessed Kennedyesque qualities.
But this yearning is always accompanied with a cynical skepticism and resentment whenever anyone, particularly the news media, annoints a new guy with the title of “the next Reagan” or “the next Kennedy” or “the next Obama.” And that’s what I think is happening with O’Rourke. The media has been gushing over this guy for the last 2 years now as “the next Obama”, discussing the magic quality of his speeches, their uplifting nature, etc etc. And there is the suspicion among many thoughtful liberals that the emperor has no clothes. Hence the resentment and criticism. However, too soon to predict how much this may hurt him.