Bernie Sanders’ upset victory in Michigan was a major shock for Hillary Clinton supporters for many reasons — not the least of which was the prior polling that showed her beating Sander by 20-plus percentage points.

But the perils of public primary polling aside, Sanders’ Michigan win suggests it’s too soon to write the Democratic socialist and his message of political revolution off. Next Tuesday’s Ohio primary will be the next major test for him to prove he has broadened his appeal and there, his attacks on her stance on trade deals may prove equally effective as they were in Michigan.

Michigan’s neighbor to the south shares its industrial heritage, bears a similar demographic mix, and even the geography of Ohio Democratic voters resembles Michigan’s. Ohio presents the same sort of electoral conditions as Michigan, and those conditions could prove just as receptive to Sanders’ criticism of trade deals.

“It has a lot of the same industry and it has a lot of the same feel of jobs being outsourced, and good jobs going away,” Michael Parkin, an associate professor of politics at Oberlin College, told TPM.

Michigan’s Democratic stronghold is urban voters in the Detroit area. In Ohio, it’s built around Cleveland, Cincinnati, and to a lesser extent Toledo.

Like Michigan, Ohio’s Democratic electorate is driven by blue collar workers, many of whom whose jobs have been threatened by globalization and a changing economy. Labor unions, while weaker than in the past, remain potent politically in both states.

The Rust Belt’s deep tie to manufacturing may explain why Sanders was able to gain traction with African-American voters in Michigan — winning about 30 percent — while elsewhere in country, he has been absolutely walloped by Clinton with the black vote.

“The reason why Bernie was able to make inroads with [black voters] in Michigan is that for a lot of them, their jobs are tied — or were tied — to the auto industry or industry in general,” Parkin said. “So an economic message resonates with them.”

It will be some time until it is parsed exactly why the top line numbers in Michigan’s polls was so off from Tuesday’s results. But according to Democratic pollster Cornell Belcher, many of the state’s underlying polling trends — Michiganders’ attitudes and values — ultimately bore out in Tuesday’s results, and show why voters turned for Sanders.

“What Bernie did [Tuesday] night was probably because of really good polling,” Belcher told TPM. “They found a persuasive issue to move voters and the issue of trade, which they effectively attacked [Clinton] on, moved voters.”

Ohio’s economy is more diversified than Michigan’s, experts said, but the general hostility to free trade agreements carries over state line.

“NAFTA is not popular in Ohio, particularly among working class Democrats,” Ohio State University political science professor Paul Beck told TPM, referring to the trade agreement signed by Clinton’s husband Bill when he was president.

In a speech Clinton delivered in Cleveland Tuesday evening as results from Michigan were still pouring in, she stressed an economic message. But she has yet to formulate an effective response to Sanders’ trade attacks.

Instead, her campaign has doubled-down on her dubious criticism of Sanders’ vote on the Wall Street bailout package that also provided relief to the auto industry. The auto industry is important in Ohio, but not to the extent it dominates in Michigan.

Having won the 2008 Ohio primary against President Obama, the Clinton campaign may have been caught flat-footed by Tuesday’s results. “[The 2008 win] led people to think that she was going to be well positioned here for 2016,” Beck said, “But I think, now, there is going to be worries.”

Ohio and Michigan both have an open primaries, which Tuesday brought independent voters who overwhelmingly favored Sanders. But in Ohio, the dynamics of the open primary will be complicated by the race on the Republican side. Ohio’s GOP Gov. John Kasich is popular there, and independent voters may prefer to vote in the Republican primary so they can help him stop Donald Trump. Furthermore, Ohio’s economy is in less dire straits than Michigan’s, and expect Kasich, as he campaigns this week, to take credit for turning it around.

“You’re going to have Kasich saying, ‘Well I have been able to maintain some more jobs and build some new jobs,” Parkin said. “It will confuse the message for voters.”

And at the end of the day, Clinton is still owning Sanders in the national delegate count. The Michigan squeaker pulled off by Sanders was offset by a Clinton landslide in Mississippi.

“He hasn’t found a really effective contrast for her nationally,” Belcher said. “But in the Rust Belt, and in those states, trade is a big deal.”