Four years ago, the Wisconsin state fairgrounds were a scene of celebration. The nation’s newly elected president, Donald Trump, stood amid red-bauble-bedecked Christmas trees and regaled thousands of supporters with tales from the night Wisconsin propelled his improbable victory.

Today, the grounds are host to a field hospital for treating coronavirus patients, row-upon-row of stark white beds to accommodate overflow from the state’s beleaguered medical centers.

Outside lies a suburban Milwaukee community that had been in the midst of a renaissance — until the novel coronavirus took hold. Restaurant owners endured whiplash as the rules of reopening were fought over in court. Police officers relived the memory of patrolling a nearby city, Kenosha, as buildings were set aflame.

To the east are a sea of blue signs for former vice president Joe Biden. To the west, it’s all Trump. In between — in the shadow of an idled Ferris wheel — voters wait to cast ballots in lines that stretch around the block.

To understand the forces roiling American politics this year, there’s one state that seems to have them all. Wisconsin has one of the nation’s fastest growing coronavirus infection rates. It has a government wracked by toxic division along partisan lines. Its top court is dominated by conservatives quick to side with Republican legislators. Its election system is under scrutiny and has already faltered. One of its largest cities has become a byword for racial injustice — and for deadly riots.

It’s the 2020 election in microcosm. So it’s only fitting that Wisconsin may be the state that decides the nation’s destiny next month.

“Wisconsin,” Chris Walton, chair of the Milwaukee County Democrats, said, “is one-stop shopping this year. We’ve got it all.”

But what it all means varies dramatically depending on geography. From the bustling lakeside shores of Milwaukee to the endlessly green dairy farms of the countryside — with a tangle of towns and suburbs sprinkled in between — Wisconsin has more than its share of ideological bubbles and battlegrounds.

“The country is divided and so are Wisconsinites,” said Reid J. Ribble, a former Republican congressman who represented the state’s northeast for three terms. “You drive through any part of rural Wisconsin and there are thousands and thousands of Trump’s signs. They’re everywhere you look. But if you get into the suburban or urban areas, you see that same level of energy on the Biden side of things.”

In Walton’s world, it’s a blue bubble: The 32-year-old said he doesn’t know any undecided voters.

Throughout the county — but especially in the city’s African American neighborhoods, he said — voters have made up their minds about Trump’s presidency. They’re determined to end it, four years after depressed turnout among Black voters helped Trump to skate past Hillary Clinton in Wisconsin by the barest of margins — less than 1 percent.

“People are mad. They’re mad with the white-hot heat of 1,000 suns,” said Walton, who is Black. “The last four years have been a disaster.”

Stacy Clark, a 29-year-old Biden campaign volunteer, has no trouble enumerating the reasons, many of which hit close to home in a city that is among the country’s most racially segregated.

There’s the pandemic that has disproportionately impacted Black communities, including in Wisconsin. There’s the brutality of police shooting a Black man in the back seven times in nearby Kenosha. There’s the president’s dalliance with white supremacists and armed right-wing groups, of which the state has its share.

“There’s just so much,” said Clark, who works in nonprofit community health care. “This president, since day one, has really amped up people to vote against him.”

On the other side of the state — in predominantly White, rural areas of the state’s northwest — views of Trump are a mirror image.

Polk County — population 44,000, hard on the Minnesota border — was once a presidential battleground, with Barack Obama coming within a few hundred votes of winning there in 2008.

Eight years later, Trump triumphed nearly two-to-one. If anything, local Republican chair Alan Walker predicts, the vote will be even more lopsided this time.

“I’ve talked to people who have never voted before in their lives. But they’re going to vote for Trump this time,” Walker, a retired agronomist, said.

The reasons are many: In a community populated by antiabortion Christians, there’s appreciation for Trump’s three conservative Supreme Court picks. There’s respect for the hard-line law and order stance he took after protests turned violent in Kenosha and, even closer to home, Minneapolis. And there’s the sense — strange as it may seem — that Trump understands the struggles of Wisconsinites who work the land for a living.

“Here is this guy from New York who probably knows as much about farming as I know about real estate,” said Cris Peterson, who runs a dairy farm in another northwest Wisconsin county, Burnett. “But he knows that farming is the backbone of this country.”

Although the Trump years have been turbulent for many farmers — and disastrous for some — Peterson said “things are looking up” on her family’s 1,000-cow farm.

That’s despite the fact that the coronavirus pandemic dealt the dairy industry a grievous blow this year, with schools and restaurants canceling their contracts and farmers dumping milk rather than putting it on an already saturated market.

Peterson said Trump’s handling of the pandemic was not to blame.

“They accused him of doing nothing. I don’t know how he could have done more,” she said. “Hindsight is 20/20. Who knew it was going to be such a big deal?”

Many in Wisconsin are only finding out now just how big a deal the coronavirus really is. Average cases are up 40 percent this month, deaths have more than doubled and hospitalizations are setting records daily — pushing the field hospital at the fairgrounds into service. Nationwide, only the Dakotas and Montana have faster growing outbreaks.

Although cases have still been somewhat limited in the northwest, other rural areas of the state are now getting hammered after earlier waves of the disease passed them by.

Yet attitudes toward basic prevention remain as polarized as the state’s politics. While masking and social distancing are common in urban centers such as Milwaukee and Madison, they are far less pervasive elsewhere.

“In the more rural parts of Wisconsin, you drive by taverns and other meeting spots and they’re just packed on a Friday night,” said Katherine Cramer, a politics professor at the University of Wisconsin at Madison.

It’s a disconnect fed not only by national politics — with the president disdaining mask use, even after he got sick himself — but also by divisions at the state level.

While Gov. Tony Evers (D) has sought to take an aggressive stance to beat back the coronavirus, with business restrictions and mask mandates, the Republican-dominated legislature has often blocked his efforts. And it has relied on a conservative state Supreme Court for help.

In April, the court overrode Evers’s attempt to halt in-person primary voting, yielding an election in which people stood in line for hours to cast their ballots during a pandemic. A month later, the court, at the legislature’s urging, struck down the governor’s stay-at-home order.

The ruling was cause for celebration among many restaurant and bar owners, who gleefully reopened after a two-month shutdown.

But not for Kirk Bangstad. The owner of the Minocqua Brewing Company in the state’s scenic Northwoods had never been political before. But the court’s rulings struck him as reckless. He reopened cautiously — outdoors, with servers wearing masks — even as other restaurants in bright red Oneida County swung their doors wide with few or no restrictions.

Bangstad said the area is now feeling the consequences, along with much of the rest of the state, as the death count rises.

“This could have been brought under control,” he said. “But instead, Wisconsin is a hot spot. And we will be for the foreseeable future.”

Bangstad was so angered by the heedlessness he saw among Republican politicians that he decided to run for the state assembly, though he gives himself little chance. He has also hung a vast Biden-Harris campaign banner on the restaurant, now shuttered for the season.

Bangstad said he has been surprised by how much support he has received, though he said he has also endured abuse.

“We’re super amped up in Wisconsin,” he said. “There’s such virulent hatred on either side.”

The heightened tension reflects the stakes: A Washington Post average of polls shows Biden eight points ahead in the state. But Clinton was also ahead in Wisconsin polls, and should Trump pull out another surprise, the loss of the state’s 10 electoral votes could be fatal to Biden’s chances.

Whether that has happened is unlikely to be known on election night. State law does not allow early or absentee ballots — of which more than 1 million have already been cast — to be counted before Election Day. Republican legislators have blocked attempts to change that.

That makes Dan Devine nervous.

The nonpartisan mayor of West Allis — the city where the state fairgrounds are located — has been heartened to see the eagerness with which voters have lined up to cast their ballots in recent days. He just wishes officials could get to work counting them so the state that best embodies this peculiar election year doesn’t leave the nation waiting to find out what it has said.

“People are turning out, which is great,” Devine said. “But we don’t want to be this year’s Florida.”