Bernie Sanders campaign deemed Michigan a “critical showdown.” | AP Photo Bernie Sanders wins Michigan in stunning upset

Vermont Sen. Bernie Sanders has won the Michigan Democratic primary, according to the Associated Press, narrowly defeating Hillary Clinton in a stunning upset.

Clinton had been widely expected to win the Rust Belt state, having led Sanders by double digits in polls leading up to Tuesday's primary.

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But the Sanders campaign deemed Michigan a “critical showdown,” and aggressively attacked Clinton for her policies on trade and her ties to Wall Street. Sanders is hoping his win in the delegate-heavy Midwestern state — second in delegates only to Texas so far — will show that his populist economic message can resonate elsewhere.

Sanders, speaking from Miami on Tuesday, hailed his “enormously successful night” in Michigan but acknowledged the likely split in the delegate haul and looked ahead to the March 15 primaries.

“I want to thank the many thousands of volunteers that we had in the state of Michigan for knocking on doors and for making the phone calls that created this kind of enormously successful night for us,” Sanders said during a brief press conference. “In the last week, we have won three caucuses — two of them were record-breaking turnouts — and whether we win or lose tonight in Michigan, basically the delegates here are going to be split up because of proportional representation.”

Sanders said that Tuesday’s standings show that his political revolution “is strong in every part of the country” and maintained that his campaign has yet to hit its best states.

“We’re gonna do very, very well on the West Coast and other parts of this country,” he said, adding that voters are tired of “a corrupt campaign finance system,” super PACs, “a rigged economy” and “broken criminal justice system.”

“What we have seen is in poll after poll, state after state, what we have done is created the kind of momentum that we need to win,” Sanders concluded. “So once again, this has been a fantastic night in Michigan. We’re very grateful for all of the support that we have gotten from the state, and we look forward to going to Illinois, Ohio, Missouri and the other states that we will be competing in next week.”

Clinton had made the water crisis in Flint, a predominantly African-American city, the focus of her pitch to Michigan voters. Although she was endorsed by the state’s two U.S. senators, Democrats Debbie Stabenow and Gary Peters, Michigan’s unions did not coalesce behind either candidate.

Exit polls showed the electorate breaking along lines similar to previous primary contests: Sanders outperformed Clinton among men and younger voters, while she did better among older voters and women.

But Sanders bested the former secretary of state among white voters, 57 percent to her 42 percent, while she beat him among black voters, 65 percent to his 30 percent. In the South, she has often carried more than 80 percent of the African-American vote.

And Sander trounced Clinton among independents, 70 percent of whom voted for Sanders.

Michigan awards its 147 delegates on a proportional basis, so they will likely be split fairly evenly between the two candidates.