No Democratic presidential candidate had campaigned in Traverse City, Michigan, in decades until Sen. Bernie Sanders pulled up to the concert hall near the Sears store on Friday. Some 2,000 people mobbed him when he arrived, roaring in approval as he called the country’s trade policies, and Hillary Clinton’s support for them, “disastrous.”

“If the people of Michigan want to make a decision about which candidate stood with workers against corporate America and against these disastrous trade agreements, that candidate is Bernie Sanders,” Sanders said in Traverse City, about 250 miles north of Detroit.

A startling upset

Sanders pulled off a startling upset in Michigan on Tuesday by traveling to communities far from metropolitan Detroit and by hammering Clinton on an issue that resonated in this still-struggling state: her past support for trade deals that workers here believe robbed them of manufacturing jobs. Almost three-fifths of voters said that trade with other countries was more likely to take away jobs, according to exit polls by Edison Research, and those voters favored Sanders by a margin of more than 10 points.

For Clinton, it was a stinging defeat in a state that she had made a symbol of her campaign, pledging to help the citizens of Flint overcome its contaminated water crisis in a rare display of passion and outrage from an often-reserved candidate. The results were also a reminder of her weakness among two key voting blocs: working-class white men and independent voters.

Clinton may rethink message

The setback will almost certainly lead her to sharpen or even rethink her economic message, which does not seem to be reaching voters who feel betrayed by the Democratic Party’s embrace of free trade and left behind by the forces of globalization and deregulation. The first big test will come Wednesday night, when the two candidates debate in Miami, and then in the major industrial states that vote on March 15, including Ohio and Illinois.

Despite the loss, Clinton still has a large lead among delegates and is likely to pick up more than Sanders on Tuesday night because of her lopsided win in Mississippi.

A big prize for Sanders

Still, Michigan was a big prize for Sanders, who had poured money and time into the state, and he is certain to capitalize on the attention it will bring. Sanders began advertising heavily about a month ago, spending nearly $2 million, while Clinton was more focused on the Super Tuesday contests held last week.

One ad, according to advisers to Sanders, was especially effective against Clinton: It portrayed Sanders as the only candidate who had consistently opposed the sort of free trade agreements that many Michigan voters blame for job losses in their state.

Sanders also seized on trade during the Democratic debate on Sunday night, a faceoff that many analysts felt Clinton had won, but that his advisers believed had conveyed his intensity and sincerity on economic fairness.

Sanders undeniable

Despite Clinton’s advantages, including the support of much of the state’s Democratic establishment, the Sanders campaign showed deft organization and strategy: Sanders crisscrossed the state, speaking to more than 40,000 people, and his campaign opened 13 offices and hired 44 staffers to carry his message. He also visited places that were largely overlooked by the Clinton campaign, including Traverse City and Kalamazoo.

Beverly Christensen, a retired pilot, said she had waited in line for a couple of hours to see Sanders at his rally in Traverse City. She called it “huge” for Sanders to come to the area, saying she could not recall another presidential contender visiting since the home-state favorite Gerald Ford stopped by.

“To have him show up here — it was like he was a superstar just coming to our small town,” Christensen, 68, said in a telephone interview. “We felt like we were being heard and being listened to, and that was really important.”

Victory in Traverse City

In Grand Traverse County, the home of Traverse City, Sanders won with about 64 percent of the vote. He also performed especially well in counties that are home to major campuses like the University of Michigan, Michigan State University and Western Michigan University.

As results flooded in Tuesday night, Sanders said he had felt the race shifting in his favor in recent days as he talked with autoworkers, union leaders and college students, who all seemed eager for a more assertive progressive agenda.

“If you understand that two weeks ago, we were 30 points behind, it is very clear, as I felt, that we have a lot of momentum with us,” Sanders said in an interview. “Many of the vibes we were getting were very, very positive. I knew, I knew that these polls that had us 20 or 30 points behind were wrong.”

Still work to do

While Michigan’s economy has recovered substantially since the economic crisis, its unemployment level has continued to hover above national averages. More problematic, some analysts fear that many have simply stopped looking for work as the state’s labor force has shrunk.

Although the auto industry, which fuels the regional economy, has rebounded significantly from the lows of 2008, Detroit only recently emerged from bankruptcy.

“He was strong and forceful on trade, and persuasive with a lot of Michigan Democrats who have seen what’s happened to their economy over the past 20 years,” said Tad Devine, a senior adviser to the Sanders campaign.

Ad wars

When Clinton accused Sanders at the debate of opposing the 2009 federal bailout of the auto industry, and then began broadcasting a radio ad about the issue on Monday morning, Sanders advisers scrambled to come up with an ad of their own, explaining that Sanders had supported the bailout but opposed earlier aid for Wall Street that included some money for car companies. While the Clinton ad was unmatched on the air for several hours, Sanders advisers said their ad was up on Monday night and covered by the Michigan news media — enough to halt the effectiveness of the Clinton spot, they argued.

Sanders’ Michigan operation ultimately drew on hundreds of volunteers to make phone calls and help transport voters to the polls on Tuesday, while other aides used a string of short advertisements — some lasting five seconds or less — to spread the message about Sanders on Facebook and Twitter.

Strongest support from white voters

Sanders performed particularly well among white voters — especially white men, but also white women — and he won independents strongly. He lost to Clinton among Democrats and minority voters.

Clinton advisers had been fearing a loss, concerned that Sanders would do especially well with white voters and swamp any advantage Clinton had among African-Americans in cities like Detroit and Flint. Clinton also sent her husband, former President Bill Clinton, and their daughter, Chelsea, to campaign on her behalf, and she had support from many Democratic elected officials. But Sanders clearly broke through with white voters, who represented about 68 percent of the Democratic electorate on Tuesday.

Worry about Ohio, Illinois and Missouri

Clinton has a formidable lead over Sanders in delegates, but her campaign leaders are worried that Sanders could upend her recent momentum if he parlays his narrow victory in Michigan into wins next Tuesday in Ohio, Illinois and Missouri, where his campaign is focusing its resources.

Clinton is competing hard in those states, as well as in Florida and North Carolina, which also vote on Tuesday. Her aides are confident that even if she loses the three Midwestern states to Sanders next week, she could still come away with more delegates that night, because her victories in Florida and North Carolina would most likely be bigger than his in the other states.