Up front, I'll admit that I'm speculating on an unsubstantiated rumor, but timing is everything and the rumor started at the ideal time to help Hillary (the end of last week), so that is where I suspect it to have originated.
The rumor is that the Repubs now have in their hands video of Michelle Obama going into a Wright-like tirade about "greedy whitey" and are saving it for the fall. If this turns out to be true, the timing of where and when this rumor started should be remembered. When you see who it was meant to help, you will have a clue as to who delivered it to the Repubs.