It's a typical white privilege argument: a black man cannot achieve anything without being the beneficiary of some advantage a white man is not privy to. Donald Trump sort of started this with his questions over Obama's school records; while republicans in the past raised the issue to question Obama's college age views or who paid for his education, Trump argued Obama was a poor student and didn't deserve to get into Harvard. Which of course insinuates that Obama, who became head of the Harvard Law Review, only got into a premier law school because he's black
And of course any pushback against the argument results in the classic "hey now, you brought race into this discussion not me!" retort.
Remember back in 08 when one of McCain's talking points was that while Obama is a great speaker, he's wrong for the country blah blah blah? Now republicans can't even acknowledge something like that, or give Obama any type of compliment. It's all apart of this long running attempt to dehumanize him at every cost. McCain played along with that too, I'm not denying it, but at least he had some sense of decency.