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Tuesday's results in Michigan showed a significant potential problem for Hillary Clinton: her advantage among African-American voters was smaller in a state outside of the South.

Exit polls in Michigan showed that the former secretary of state won about 68 percent of the black vote. That was a large margin over Bernie Sanders, but Clinton had won more than 80 percent of the black vote in states like Alabama and Georgia. About 90 percent of black voters in Tuesday's primary in Mississippi backed her.

And while the exit polls are just surveys and are at times inaccurate, the actual voting returns in Michigan tell a similar story. Wayne County, which includes the city of Detroit, is about 40 percent black. Clinton won about 60 percent of the vote there.

While that is a substantial margin, voters in other large, urban counties with big African-American populations have been much supportive of Clinton during the primary process.

For example, in Hinds County, Mississippi, which includes the city of Jackson, Clinton won 83 percent of the vote on Tuesday.

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In earlier primaries, she won 71 percent of the vote in Fulton County (Atlanta), 82 percent in Jefferson County (Birmingham, Alabama), 80 percent in Shelby County (Memphis).

Statewide in Michigan, Clinton lost by about 15,000 votes. If she had won 70 percent in Wayne County, she would have likely carried the state.

While Sanders’s narrow victory in Michigan did little for him in terms of closing Clinton’s delegate lead, it does suggest a path for him forward.

Many of the upcoming primaries will be in states like Michigan, where the black vote will be between 15 to 30 percent of the electorate. They will be not virtually absent from the electorate (Iowa, New Hampshire) or dominant (Alabama, Mississippi).

On March 15, primaries in Florida (19 percent in 2008), Illinois (23 percent) Missouri (15 percent) and Ohio (18 percent) will have black populations that make them states where either Clinton or Sanders could win.

But Sanders need to start winning states resoundingly to catch up in delegates. He would greatly benefit from closing the margin between he and Clinton among African-Americans, since the Vermont senator is already winning about 60 percent of the white vote in many states.

How can he do it? Clinton seemed poised to do very well among black voters in Michigan. She had made the crisis about elevated lead levels in Flint’s water one of her top campaign issues. The mayor of Flint had endorsed and praised Clinton for her advocacy.

So it's not completely clear why Clinton did not receive as much support with black voters in Michigan. Sanders appealed to Michigan's black voters in similar ways to his approach in the South, which was very unsuccessful.

Are black voters in the rest of the country less pro-Clinton than in the South? The limited exit poll data did not provide any obvious explanations. Michigan is the only state with a large black population outside of the South that has voted so far.

A black electorate that was more male and younger would benefit Sanders, since Clinton is more popular with women and older voters. But the exit poll data suggested the vast majority of black voters in Michigan were female, just as in other states. Sanders won 30 percent of black women in Michigan, after failing to win even 20 percent of that bloc in several Southern states.

There was little data breaking down blacks by age.

If such a regional split emerges, with blacks in the South voting differently than the rest of the country, that would be a shift from 2008. Back then, Barack Obama won more than 80 percent of black voters in virtually every state.