The Bernie Sanders coalition -- a mix of young voters, liberals and independents -- is still a potent force in the Democratic primary race.

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With his unexpected win in Michigan's primary on Tuesday, Mr. Sanders proved his voting base still has power, just as the nominating calendar is about to turn to similar Midwestern states, including Ohio, Illinois and Wisconsin.

Mr. Sanders's voting base had little visibility in Mississippi on Tuesday, where Hillary Clinton won an overwhelming victory on the strength of African-American voters, who made up more than 60% of the voter pool.

But in Michigan, where black voters accounted only for about one-quarter of the electorate and gave Mrs. Clinton less of a boost, the Sanders coalition held far more sway.

Mr. Sanders carried a commanding 8 in 10 voters under age 30, according to preliminary results of surveys of voters after they cast ballots. He won more than two-thirds of voters under age 45. And while Mrs. Clinton won a lopsided share of African-American voters, Mr. Sanders won nearly 6 in 10 white voters, according to exit polls reported by CNN and other media.

A similar coalition could make for close races in other Midwest states with manufacturing roots, where the voter pools look more like those of Michigan than of other states that have voted so far.

Its white, non-Hispanic population, at 76% of all residents, looks similar to the 80% share of white residents in Ohio, 78% in Pennsylvania and 82% in Wisconsin. The percentage of people 25 or older with a bachelor's degree, at 26%, is in line with those three states.

Mr. Sanders has already won one upper Midwest state, Minnesota, where Democrats held caucuses rather than a primary.

The Tuesday night results have a message for both Democratic candidates. For Mrs. Clinton it is that her campaign needs a rationale and message as compelling as Mr. Sanders's call for a "political revolution" against the wealthy and Wall Street, which has caught the imagination of the party's liberals and young voters.

For Mr. Sanders, it is that winning the nomination in a racially diverse party is difficult without winning support from nonwhite voters.

Mr. Sanders's weak support among African-Americans has severely hampered him in the South, but he may find diverse states outside the South to be friendlier ground. He won 30% of African-American voters in Michigan, his best showing in any state for which there are exit polls and a far larger share than the single-digit support he had drawn in several Southern primaries.

As in other Southern states, Mrs. Clinton's victory in Mississippi rested on support from nearly 9 in 10 African-American voters, exit polls showed.

Donald Trump carried Mississippi's Republican primary. Like Mrs. Clinton, he has won the contests in Southern states, including those in Georgia, South Carolina, Tennessee and Virginia.

As in prior contests, Mr. Trump's support was strongest among voters without a college degree and those on the lower end of the income scale. But he swept almost every other group as well, even expanding the coalition that had delivered other Southern states to him.

Mr. Trump won among Republican Party members and independents who cast ballots. He carried evangelical Christians and non-evangelicals, foiling Sen. Ted Cruz, who had hoped to build a lead among evangelicals. Mr. Cruz, a favorite of social conservatives, carried voters who rated themselves "very conservative," as he had in prior contests.

(END) Dow Jones Newswires