No good deed goes unpunished.
The President (as Chief Executive of the US Governement)cannot apologize for slavery since the United States Government did not engage in slavery. Individual plantation owners and slave traders and the southern states held humans in slavery and committed this inhuman crime. The United States government opposed slavery at the same time that several states made it legal. When those states were challenegd by Lincoln, they tried to resign from the United States and establish their own Confederacy.
It seems to me blacks should embrace the United States for emancipating their ancestors from the inhumanity of slavery instead of acting like personally involved victims.