It is indeed reprehensible in its call for racial solidarity. I would just add that the call for African Americans to “have his [that is, President Obama’s] back” is a not-so-subtle suggestion that the President’s critics are (a) threatening him with something more than just criticism, and (b) doing so in a somehow cowardly and unfair way. So if you’re black and you don’t support the President, well then you’re practically just standing around with your hands in your pockets while a brother gets lynched. No? Well, you explain why that phrase was used then.