In the final stretch of the 2016 campaign, Paul Maslin could sense that former Sen. Russ Feingold was in trouble, as the Wisconsin Democrat tried to win back his Senate seat from Republican incumbent Sen. Ron Johnson.

“I could feel Johnson found a message groove and Russ was doing sort of a victory lap,” said Maslin, a Democratic consultant in the Badger State, who was doing work for the independent expenditure arm of the Democratic Senatorial Campaign Committee.

Still, Maslin said he missed signs that Democratic presidential nominee Hillary Clinton would lose Wisconsin, a state Republicans had not won since President Ronald Reagan’s landslide re-election in 1984.

Many Democrats never expected her to lose, either. Or that she would lose Ohio, which went for Barack Obama in 2008 and 2012 after voting Republican the two previous elections. Or Michigan and Pennsylvania, both of which hadn’t voted for a GOP presidential candidate since George H.W. Bush in 1988.

Had Clinton won those states, it would be her taking the oath of office next week instead of President-elect Donald Trump.

But Clinton never visited Wisconsin and paid scant attention to Michigan, while she was trying to expand the electoral map in red states.

“They didn’t have to lose Wisconsin and Michigan,” Maslin said.

Democratic Rep. Tim Ryan said he saw it coming while he was campaigning for his own re-election in Ohio’s 13th District.

“I would stand outside at plant gates and steel mills and shake hands. You did get a sense you were losing some people,” Ryan said.

Trump connected with working class voters in the Rust Belt by blaming free trade agreements like NAFTA and the then-pending Trans-Pacific Partnership for the loss of jobs there. And Republican voters in general have followed his lead: from 51 percent favoring free trade in 2015 to two-thirds opposing it, according to a Pew survey released in October.

Clinton’s onetime support for the TPP cost her votes there. And her backtracking on the agreement, which she once famously called the “gold standard” for trade agreements, lowered her trustworthiness ratings.

Democrats already have a heavy lift in 2018 when they will be defending at least ten vulnerable Senate seats. And four of them are in Rust Belt states that twice voted for Obama but switched to Trump last year. 

But the Democratic Senate incumbents in Ohio, Michigan, Wisconsin, and Pennsylvania have deep ties to working class white voters in their states, and experts say 2018 will be different there than 2016.

Ohio

Democratic Sen. Sherrod Brown could face a tough rematch against Republican state Treasurer Josh Mandel. 

Trump won Ohio last year by 8 points and Republican Sen. Rob Portman won his Senate race against Democratic former Gov. Ted Strickland by 21 points, despite Portman’s perceived vulnerability at the beginning of the cycle.

But Brown has structural advantages in the Buckeye State that Clinton and Strickland didn’t have. And while Obama carried Ohio by 3 points in 2012, Brown won his race against Mandel by twice that margin.

Unlike Clinton, Brown has been a consistent critic of free trade, even writing a book on the subject back in 2004, called “Myths of Free Trade.”

“Sherrod Brown literally wrote the book on standing up to China and creating a trade agenda that puts America first,” said Jake Strassberger, a spokesman for the Ohio Democratic Party.

Mandel has already tried co-opting Trump in his campaign message, with references to a rigged system in Washington. But Republican political consultant Bob Kish warns it would be hard for Mandel to appropriate Trump’s language.

“If I’m Josh, I kind of take trade out of it,” Kish said.

Rather, Kish said, the best way to beat Brown is to focus on cultural issues like abortion in running against a liberal, instead of on his record on labor.

Michigan

To defeat three-term Democratic Sen. Debbie Stabenow, a viable Republican challenger “would have to be a populist, not a National Review Republican,” according to Greg McNeilly, a Michigan GOP strategist and former executive director of the state party. 

“They have to be for the Second Amendment and for the working class in a way that goes beyond the platitudes, but really take it to her,” he said.

Stabenow defeated longtime Republican Rep. Peter Hoekstra by 21 points in 2012. And McNeilly suggested that last November’s results in the Wolverine State was as much about the Democratic candidate as about the issues, pointing to the weak turnout for Clinton in Flint, where Democrats have fought for funding to fix the city’s drinking water crisis.

“If you can’t get the people of Flint excited, can’t get them engaged, then your candidate is just not mobilizing people,” he said.

McNeilly said, so far, a credible Republican challenger to Stabenow has not emerged, something that would have to happen in roughly the next 90 days for the GOP to have a chance.

Wisconsin

Despite Trump’s inflammatory rhetoric, some of the Wisconsin voters who supported him had voted for Obama four years earlier, Maslin, the Democratic consultant, pointed out. What’s more, the same voters also elected Democrat Tammy Baldwin as the first openly LGBT senator.

“How sexist and racist are they that they voted for the black guy and the lesbian?” he asked. 

For the next two years, Maslin said Baldwin would need to channel liberal populism in the manner of Vermont independent Sen. Bernie Sanders, who won the state’s Democratic presidential primary last year.

“Anything short of that and she is in danger of becoming tomorrow’s status quo,” he said. “Bernie, even more than Obama, he was the most popular political figure.”

Maslin also said simply opposing Trump won’t cut it.

“No is not enough,” he said.

Pennsylvania

Talking about wages and jobs should be a safe bet for two-term Democratic Sen. Bob Casey, said Kevin Washo, who served as executive director of the Democratic National Convention’s host committee in Philadelphia last year. 

On his way to a 9-point win over Republican challenger Tom Smith in 2012, Casey won in counties outside urban areas that Obama lost that year, such as Berks and Chester County in the southeastern Pennsylvania, and in Beaver County and Fayette County in the southwestern part of the state.

While Clinton’s loss in the Keystone State last year has been attributed to her disconnect with the white working class, Washo said Casey has a bond with those voters.

“People are wringing their hands about it because they don’t understand it,” he said. “He’s one of the people who is not wringing his hands because he gets it.”

Like the other three Rust Belt Democrats, Casey has frequently been a critic of free trade and has called for tightening restrictions on currency manipulation, something Trump now espouses.

“He is going to be in better shape than some because Sen. Casey has been talking about jobs,” Washo said.