You know the story well: Not a single public poll in 2016 showed Donald J. Trump beating Hillary Clinton in Wisconsin, and forecasters suggested he had almost no shot. FiveThirtyEight gave him less than a one-in-six chance of winning the state.
But after the votes were counted, with turnout down in key Democratic areas, Mr. Trump eked out a victory by fewer than 30,000 votes.
This year, again, virtually every poll has shown the Democrat, Joseph R. Biden Jr., with at least a slight edge over Mr. Trump. A New York Times/Siena College survey last month gave Mr. Biden a five-percentage-point advantage among likely voters. Polls taken since then by CNN and NBC News/Marist College have each given Mr. Biden an outright, 10-point lead.
And with the coronavirus now raging in Wisconsin, particularly in the politically competitive northeastern region, Mr. Trump faces an uphill battle toward repeating his victory from four years ago.
“Certainly, with the sharp rise in cases here, it’s on the agenda for voters,” said Charles Franklin, a political scientist who runs the Marquette Law School poll, which is seen as the definitive political survey in the state. “His handling of Covid does appear to be having a bigger effect on people’s vote than either the economy or his handling of the protests.”
And concern about the pandemic has ticked upward recently. More than six in 10 Wisconsin voters in a recent Marquette poll described themselves as at least fairly worried — including 27 percent who said they were very worried, up from 21 percent last month. Fully 50 percent of Wisconsin voters said they did not expect the virus to be under control for at least another year, running counter to Mr. Trump’s insistence that it is already being handled effectively.