GREEN BAY, Wis. — The presidential race on Friday barreled into the Upper Midwest, the candidates arriving at the epicenter of the nation's latest coronavirus outbreak and showcasing dramatically different campaign approaches on one of the busiest days of the general election.

Beginning a last frenzy just four days before Election Day, both candidates put forward their closing arguments in an area of the nation expected to be as critical to the winner as it was in 2016. But they argued their cases against a dour backdrop, with each of the states they visited seeing rapid rises in new coronavirus cases. For President Trump, the day tested his ability to glide past criticism that he is mishandling the global pandemic even as Democrat Joe Biden emphatically denounced it.

“We’ve now hit 9 million cases nationwide, a tragic milestone,” Biden said at the start of a drive-in rally in Des Moines. “And millions of people are out of work, on the edge, and they can’t see the light. It just looks dark right now for them.”

Friday marked a newly brisk pace for Biden, who traveled to three states, a record for him in a general-election campaign in which he has been far more conscious than Trump of following health protocols related to the coronavirus. It was also Biden’s first trip back to Iowa since his dismal fourth-place finish in the state’s caucuses last winter — only this time he returned as a nominee trying to expand the electoral map in a state Trump easily carried four years ago.

“Donald Trump has waved the white flag, he’s surrendered to this virus. But the American people don’t give up,” Biden said at the Iowa State Fairgrounds, as car horns honked throughout and, at one point, two eagles flew overhead. “We don’t panic. He panicked!”

Biden displayed a mask and urged people to put one on, saying: “This isn’t a political statement. It’s a patriotic duty, for God’s sake.”

At the same time, 600 miles away in Waterford Township, Mich., Trump looked out to a large, packed crowd, many of its members not wearing masks, as is typical for his events. When the president spotted Fox News host Laura Ingraham, he was incredulous that she had a face covering.

“No way!” he said from the stage. “She’s wearing a mask? She’s being very politically correct!”

Trump mocked Biden for focusing so much on the coronavirus response, and he ridiculed the Democratic governors in the states he was visiting for past restrictions meant to prevent more cases, including attempting to limit the number of attendees at Trump’s rallies.

He repeated his baseless accusation that doctors are inflating the number of patients they diagnose with covid-19 to make more money, even as he campaigned in states where officials and local media blared with fears about overrun hospitals.

“You turn on the news: covid, covid, covid, covid, covid,” Trump said, then repeated a false claim that testing was responsible for the increasing number of cases. “And you know, cases are up — why are cases up? Because we test more than anybody in history.”

He pointed to himself as an example of how Americans can recover — “Superman! Superman!” the crowd chanted in Green Bay, Wis. — and he ridiculed Biden for saying that as president he would consider new closures if scientists demanded them in virus-ridden locations.

“You’ll have no school,” Trump said. “No graduations. No weddings, no Thanksgiving. No Christmas. No Fourth of July. There will be no nothing. No future.”

Biden countered such claims during his events, as the candidates engaged in a long-distance back and forth.

“I’m not going to shut down the economy,” the Democrat said in Des Moines. “I’m going to shut down the virus.”

On his next stop, in St. Paul, Minn., Biden expressed outrage at Trump’s suggestion that doctors are exaggerating the number of covid-19 deaths.

“Did you hear what he said today?” Biden shouted over the sound of airhorns from nearby Trump supporters. “The president of the United States is accusing the medical profession of making up covid-19 deaths! Doctors and nurses go to work every day to save lives. They do their jobs. Donald Trump should stop attacking them and do his job.”

Biden grew visibly annoyed by the pro-Trump protesters, at one point referring to them as the “ugly folks over there beeping the horns.”

“They are not very polite, but they’re like Trump,” Biden said.

The Democratic governors of all three Upper Midwest states Trump visited Friday have imposed varying degrees of coronavirus restrictions, although none are closed down to the extent the president suggests. Cases are rising in every swing state, with Michigan’s up more than 90 percent in the past two weeks, Minnesota’s up nearly 55 percent and Wisconsin’s up about 40 percent.

The increasing coronavirus caseloads have been especially alarming in Minnesota and Wisconsin, as well as in Michigan’s Upper Peninsula, all places that had managed to avoid the worst of the deadly surges this summer.

Polls have indicated that Biden has a wider pathway toward victory, but there is deep apprehension among Democrats in the final days of the race, as they worry they are captive to the same false optimism they felt four years ago.

While early-voting numbers have indicated Democratic enthusiasm, there are lingering questions about whether Biden can persuade those who did not vote for Hillary Clinton in 2016 to return to the polls. Trump’s campaign has expressed public optimism in recent days, but it is still banking on a large in-person turnout on Election Day.

Stoking some Democratic concerns, Biden on Friday campaigned in Minnesota, a state that no Republican presidential candidate has won since 1972. His appearance elevated fears that his campaign is worried about the state, where polls have given him a steady lead.

Although Clinton carried Minnesota by only about 1.5 percentage points four years ago and Trump has eyed it as a pickup, Democrats have largely felt that it was safe enough that Biden could turn to traditionally Republican states like Georgia, Arizona and Texas.

“No, I’m not concerned,” Biden told reporters at the start of the day. “We’re going to be in Iowa, we’re going to be in Wisconsin, so I thought I’d stop in Minnesota. I don’t take anything for granted. We’re going to work for every single vote up till the last minute.”

Biden leads Trump by 10 percentage points nationally, 53 percent to 43 percent, according to a Washington Post average of national polls since Oct. 12. Biden’s margin in Wisconsin and Michigan is nine points. It is seven points in Pennsylvania, five in Arizona and one in Florida.

Recent polls have shown that some White voters without college degrees, the mainstay of Trump’s political support, have pulled away from him in Michigan. The state represented a surprise if exceedingly narrow victory for Trump in 2016 and is a key element of his reelection strategy.

The president’s pitch throughout the day rarely mentioned the health impacts of the coronavirus, instead focusing on the foreign business ties of Biden’s son Hunter, the anti-police-brutality protests in cities that have at times turned violent and the economic risks of keeping businesses closed because of the pandemic.

In Waterford Township, an enthusiastic crowd huddled outside an airport hangar as Trump delivered an upbeat prediction of victory on Tuesday and attacked both Biden and Gov. Gretchen Whitmer (D).

“Biden will eradicate the economy. I will eradicate the virus and make the economy better than it ever was,” he said.

Recent polling has found that concerns about the coronavirus have weighed heavily on Trump’s candidacy. When it comes to handling the pandemic, Biden is trusted more than Trump by double digits in both Wisconsin and Michigan, and large majorities support their state’s rules on masks and restrictions on businesses and public gatherings, according to polls.

On another front, Trump promised to return automotive jobs to Michigan and said Biden, as vice president, had overseen the exit of auto plants and jobs. When Trump complained about lockdowns and other restrictions imposed by some Democratic governors, including Whitmer, the crowd erupted in a chant of “Lock her up!”

Trump smiled but did not join in.

“I don’t think she likes me very much, and you know what? I’ve done a good job for her” in marshaling federal resources for Michigan, he added.

In Green Bay, Trump reveled in the chant “We love you!” and joked that it shouldn’t run on too long or he might start crying. And he drew laughs and cheers when he departed from his script to jokingly tell the crowd that he is the second-most-famous person in the world, after Jesus.

His mood was far darker a few hours later at a rally in Rochester, Minn., speaking to a comparatively small crowd of 250 people who were spread out to allow for social distancing, in accordance with state guidelines. Before cutting his remarks short after about 20 minutes, Trump said restrictions that forced him to address a sparse group — for which he blamed Gov. Tim Walz (D) — would be the reason he wins the state.

“Get out and vote,” he said, “And remember what your governor did tonight.”

Earlier, Trump said Biden is feebleminded and could be easily manipulated as president. “Let’s face it, he’s shot,” Trump, 74, said of Biden, 77.

Biden alluded to remarks Trump made last year claiming that American forces took over airports during the Revolutionary War, more than a century before airplanes were invented.

“And he talks about mental acuity?” Biden said. “The stable genius says wind power causes cancer.”

“It’s the same guy who said — by the way, you think I’m making this up — when he was advised about the increasing hurricanes coming across the Atlantic because of the warm water, he said maybe we should drop a nuclear weapon on them,” Biden added. “Holy mackerel.”

Biden on Saturday is slated to campaign in Michigan with former president Barack Obama before focusing tightly on Pennsylvania, a state seen as a must-win for Trump.

Biden plans to deliver a speech in Philadelphia on Sunday before campaigning across the state with his running mate, Sen. Kamala D. Harris (D-Calif.), and their spouses, Jill Biden and Doug Emhoff.

Pennsylvania is among three Rust Belt states — along with Wisconsin and Michigan — that Trump carried by less than one percentage point in 2016 in assembling his electoral college victory over Clinton. Trump is also heavily focused on the state.

Biden offered an implicit criticism of Clinton on Friday night for not campaigning in Wisconsin in 2016, telling a small crowd in Milwaukee that he would not take the state for granted. “For a whole lot of reasons — not all of which were her fault — we ended up not taking it as seriously,” he said. “We thought it was different. I’ve been here a lot. And by the way…if I get elected, I’m coming back.”

Biden is likely to spend election night near his home in Wilmington, Del., while Trump said Friday that he is considering moving an election-night party planned at his Washington hotel to the White House, citing local restrictions on the size of gatherings because of the pandemic.

“We haven’t made a determination,” the president told reporters as he left the White House to campaign, falsely depicting D.C.’s rules. “You know Washington, D.C., is shut down. . . . I don’t know if you’re allowed to use it or not.”