Here’s what I find so sweet.
Hillary can’t win w/o strong black support. If she challenges Obummer she might win the nomination...and alienate a lot of blacks.
Obummer can’t win w/o a strong showing amongst whites. And polls show that he has lost a lot of white support.
The only real chance that Hillary has is if something bad happens to the President that would prevent him from running again. (Death, Illness, Scandal, Double digit unemployment.)
And so he and /or Michelle endorse Hillary.