I really don't know what to say to those of you who are asking how the term is racist. I've lived in the South all my life (if you call Florida part of "the South") and it is simply a well known racial epithet. Its basically one rung below the n word, really.
Those of you saying you did not know that -- I don't know if you are being serious or if the phrase had become so toxic and you are so young that it had not been used before, or exactly what the issue is.
But its truly recognized universally to be racial.
As to the comment that it is used to "refer to a sticky situation," um, no, He might have been thinking that -- I can't say. But you can call a situation "tarry" or "sticky." Calling the president a "tar baby" is either a racial angle coming out that he didn't mean to, or he's just a complete idiot.