Democrats just scored a big upset in Wisconsin. But in the 2020 presidential race, the state makes them nervous.

Democrats won a major victory in Wisconsin last week, electing a liberal to the state Supreme Court despite the coronavirus disruption that closed 175 out of 180 polling places in Milwaukee, the party’s stronghold.

But when it comes to beating President Donald Trump this fall, the Badger State still worries many Democrats.

Of the Pennsylvania-Michigan-Wisconsin “blue wall” trio that Trump won in 2016 and that could again decide the 2020 election, Wisconsin may represent Democrats’ toughest climb.

Compared to the other two Rust Belt swing states, Wisconsin’s electorate is whiter and has a higher share of white people without college degrees — Trump’s most supportive demographic. Wisconsin’s wealthy and populous suburbs, meanwhile, haven’t seen the same drastic shift toward Democrats as similar communities outside Philadelphia, Detroit, and elsewhere.

All three states are expected to be tight through November’s general election, but for some Democrats, Wisconsin presents the nightmare scenario. If Joe Biden flips only Pennsylvania and Michigan, and the rest of the political map remains the same, Trump will amass 270 electoral votes — exactly the number needed to win a second term.

“I remain optimistic that Biden will carry Pennsylvania and Michigan (and every Hillary-won state) given the trends of the past several years ... but very uncertain about Wisconsin,” Philadelphia-based Democratic strategist J.J. Balaban wrote in an email.

Balaban pointed to double-digit Democratic wins in Pennsylvania and Michigan gubernatorial races in 2018, while in Wisconsin Democrats won the governor’s office by about 1 percentage point. (In Wisconsin, Democrats were facing an incumbent Republican, unlike in Pennsylvania and Michigan.)

» READ MORE: Before Pennsylvania votes, Joe Biden, Bernie Sanders face a similar test in Michigan

In a breakdown of the electoral map earlier this month, analyst Nathan L. Gonzalez rated Pennsylvania and Michigan as “tilt Democratic.” Wisconsin was one of four “toss-ups."

“Democrats did very well here in the 2018 midterm. There were five statewide offices on the ballot and they won them all, but they won them by the narrowest of margins,” said Barry C. Burden, a political scientist at the University of Wisconsin-Madison. “They were Democratic victories, but not as decisive as in Pennsylvania.”

There’s a reason Democrats chose Milwaukee for their 2020 national convention, four years after Hillary Clinton failed to visit Wisconsin during her campaign.

Given their similar demographic and economic profiles, Pennsylvania, Michigan, and Wisconsin will likely behave in similar ways in 2020. Each was decided by less than a percentage point in 2016. But with such tight margins, it wouldn’t take much of a difference to land one state in the blue column, and another in the red.

» READ MORE: Despite coronavirus, Wisconsin is holding an election Tuesday. It could hold lessons for Pa. and N.J.

An average of recent polls compiled by the Real Clear Politics web site shows Biden leading Trump by 4.4 percentage points in Michigan, 3.8 in Pennsylvania, and 2.7 in Wisconsin.

Independent analysts and strategists in both parties attribute the slight differences to Wisconsin’s demographics. The state is 87% white, compared with 82% in Pennsylvania and 79% in Michigan.

White voters who do not have college degrees made up 55% of the electorate in Wisconsin’s 2018 elections, about 10 percentage points more than in Pennsylvania and Michigan.

“Demographically, Wisconsin starts in a place that’s a little more open to Republicans,” Burden said. “These are not giant differences, but it doesn’t take giant differences for the state to be a little more competitive.”

In Wisconsin, there’s “a very small, select group” of maybe 200,000 to 300,000 voters “who dictate who’s going to win or who’s going to lose,” said Keith Gilkes, a Republican strategist based in Madison.

Paul Maslin, a Madison-based strategist who grew up in Chester County, said Democrats can’t count on the same leftward swings in suburbs that have happened in Pennsylvania and many other states.

“The Philadelphia suburbs have changed dramatically in the last 20, 25 years,” Maslin said. Outside Milwaukee, it’s “still like the old days.”

» READ MORE: Suburbs like Philly’s powered Biden’s big wins over Sanders: ‘I’m not looking for any kind of revolution’

While analysts saw some softening of Republican support in the pivotal suburbs of Waukesha, Ozaukee, and Washington Counties, it hasn’t collapsed in the same way as in other upscale suburbs around the country. “They still vote routinely 65% Republican,” Maslin said.

Priorities USA, one of the leading Democratic super PACs, still sees Pennsylvania as the “tipping point” state, the one most likely to deliver the decisive electoral votes, though it sees Wisconsin and Michigan as similarly close, and important.

The main Trump super PAC, America First, also lists all three as core states.

While Democrats rejoiced in a state Supreme Court victory, tallied Monday, analysts and strategists said it would be risky to extrapolate too much about the presidential race, given the unusual and dangerous circumstances of an April 7 election held amid a statewide stay-at-home order.

But some Democrats argued that in the first primary since the coronavirus’ impact was truly felt, there were signs that the crisis, and the federal response, are taking a toll on Trump.

When Priorities USA tests ads to gauge public reaction, sometimes the spots provoke a backlash that increases Trump’s support, said Nick Ahamed, the group’s director of analytics. But that hasn’t happened with the coronavirus ads it has been blasting onto swing state airwaves, including Pennsylvania’s, attacking Trump’s handling of the issue.

“We haven’t seen a single coronavirus ad backlash,” Ahamed said. “It’s taking things that people already thought about Trump and making it crystal clear about how that affects their lives.”

He added that the Democratic turnout in the face of difficult circumstances in Wisconsin showed that the coronavirus at least hasn’t dampened enthusiasm in what both parties expect will be a high-turnout election.

Gilkes also pointed to the toll of the virus, noting the impact on a state that depends heavily on agriculture and manufacturing. Prices are depressed for Wisconsin’s famous dairy products, he said. Trump’s efforts to restart the economy are “going to be vitally important."

Of course, Biden could lose Wisconsin and still win the presidency through other routes.

He has early polling leads in Arizona, whose 11 electoral votes could effectively replace Wisconsin’s 10. Florida or North Carolina, two other toss-ups in Gonzalez’s ratings, could also tilt the outcome. A handful of other states loom as potential battlegrounds.

But most Democrats see the Pennsylvania-Michigan-Wisconsin trio as their most straightforward path to the White House. Each had long histories of supporting Democrats for president until 2016, and each showed Democratic rebounds in 2018.

“Arizona is trending more favorably to Democrats," Balaban said, “but it’s tough to know if it’s moving fast enough to place your chips there.”