From Steve Sailer:
In other words, St. Louis got stuck with lots of African-Americans, while richer cities like New York were pawning black Americans off on lower rent cities like St. Louis using Section 8 housing vouchers. That’s a big part underlying reason for elite immigration enthusiasm — a hope that immigrants will show up and make American blacks go away. In New York, it’s been working. The number of American-born blacks in NYC has been falling since 1979.
I think DC is following the same pattern, though it’s starting with a much larger population (relatively) of African-Americans.