It's the same reason, gerrymandering of the districts (along with pre-existing racial segregation) leads to precincts which are overwhelmingly minority voters:<quoted text>
Maybe when we figure that one out, we can then proceed to calculating how Mitt Romeny didn't receive one vote in districts such as here in Cuyahoga County. Sure, I can understand a majority or even a very strong majority in Democrat districts, but not one vote?????
"All the Cuyahoga County precincts in which Romney was shut out are in neighborhoods with heavily African-American or Latino populations.
An NBC/Wall Street Journal poll in August underlines the significance of that demographic. It showed Obama leading by a 2-to-1 margin among Hispanic voters and had his support at 94 percent among black voters, with zero percent favoring Romney. Six percent said they were undecided or had no opinion. None of the poll's 120 black respondents picked Romney.
An election day exit poll by NBC News found that black voters in Ohio picked Obama over Romney by 96 percent to 3 percent. That percentage matches the spread by which Obama won in Cleveland precincts east of the Cuyahoga River."