The Wisconsin Supreme Court blocked Gov. Tony Evers’s executive order suspending in-person voting in Tuesday’s elections, launching a final scramble for election officials to prepare polling places and protect voters and workers hours before balloting was scheduled to begin.

The decision came the same day Evers (D) issued the order, which had prompted an immediate legal challenge from Republican lawmakers who argued that postponing the election would sow confusion. In a 4-to-2 decision, the state court offered no explanation for the ruling.

The rapid-fire series of developments unleashed a torrent of confusion across Wisconsin. After Evers issued the order, some local governments announced that voting was canceled, while state officials urged election clerks to proceed as if the polls would open. Legal experts, meanwhile, questioned whether Evers’s actions were constitutional.

“Unfortunately, they turned the health of our state into a political issue,” said Lois Frank, the village clerk in tiny Cambria, in eastern Wisconsin.

The bitter showdown presented a grueling test case for other states planning primaries during the coronavirus pandemic, not to mention the November elections. It also foreshadowed the likelihood that Wisconsin, by some measures the most important presidential battleground state, could become the epicenter of partisan rancor as the health crisis continues to upend the 2020 race.

The U.S. Supreme Court on Monday blocked a lower court’s six-day extension of the receipt deadline for mailed ballots, turning aside pleas from Democrats that thousands of the state’s voters will be disenfranchised because of disruptions caused by the pandemic. The ruling was 5 to 4, with the court’s conservatives in the majority.

Citing the intensifying threat of the virus, Evers on Monday afternoon had ordered the postponement of in-person voting and the receipt deadline for mail-in ballots to June 9.

He said he made the decision to act unilaterally because of dire warnings by the White House over the weekend, when several Trump administration officials predicted that infections would worsen dramatically during the coming week. Mass cancellations by poll workers, and subsequent consolidation of voting sites, also diminished the prospect for safe elections, he said.

“At the end of the day, this is about the people of Wisconsin,” Evers said in an interview . “They frankly don’t care much about Republicans and Democrats fighting. They’re scared. We have the surgeon general saying this is Pearl Harbor. It’s time to act.”

The abrupt move came after the GOP-controlled state legislature had refused to postpone the vote during a special session Evers called on Saturday.

Shortly after Evers issued the order, Assembly Speaker Robin Vos tweeted: “We don’t live in a banana republic where the executive can just cancel elections because he doesn’t want to hold them.”

The day’s events left voters and local election officials reeling — and left open the questions of how many poll workers would show up Tuesday, how many polling sites would be able to open and whether sufficient precautions would be possible to prevent the spread of the pandemic.

Members of the Wisconsin Election Commission huddled in a tense emergency meeting Monday evening, expressing uncertainty about how to enforce the U.S. Supreme Court’s ruling ordering that all absentee ballots be postmarked by Tuesday. A lower court had ordered election officials to accept ballots received as late as April 13 but did not set a postmark deadline, which would have allowed voters to cast ballots after Election Day.

“We failed them,” Democratic appointee Ann S. Jacobs said of voters, “and the glee with which this is being extolled as a victory is astonishing.”

As of Monday, Wisconsin had reported 2,440 confirmed coronavirus cases and 77 fatalities. State officials said the real numbers may be much higher and that moving ahead with the election would only accelerate the spread.

“I just hope people keep us in their thoughts and prayers because, on that day, we’re going to be on the front lines just like the health-care workers,” said Frank, the Cambria clerk, who has health issues and has been forced to defy her doctor’s orders to stay home to avoid infection. “I just personally know a lot of clerks that do have health risks, myself included.”

Ted Faust, who resigned in protest as clerk of Waterloo Township last week and urged his county’s other clerks to do the same en masse, said holding the election “doesn’t seem sensible whatsoever.”

“It seemed to me that things had developed into a contest for political advantage between the governor and the legislature, with we clerks being the pawns in between,” Faust said. “It just feels like you’re being used.”

Jay Heck, the executive director of Common Cause of Wisconsin, said he was “terrified” by the idea of the state holding the election Tuesday, given the mounting health risks.

For the first time in nearly 25 years in his role, he is not encouraging people to vote in person, which “flies in the face of everything I believe in.”

“It’s insanity. It’s just insanity,” an emotional Heck said midday Monday, before the governor’s order, describing the ways people could contract coronavirus at a polling place. “It makes me cry thinking about what is going to happen tomorrow. It really does.”

It appeared that the results of Tuesday’s vote would not be immediately available. Meagan Wolfe, the state election administrator, said late Monday that she is instructing clerks not to report election results until 4 p.m. on April 13 and that releasing any totals before then would violate a federal court order issued last week.

Tuesday’s contests include the Democratic presidential primary between former vice president Joe Biden and Sen. Bernie Sanders (I-Vt.), as well as local elections and a high-stakes contest for the state Supreme Court, which features a conservative incumbent facing a liberal challenger.

Whether Evers had the authority to postpone the elections had became the subject of heated debate in Wisconsin. As recently as Friday, amid widespread calls that he act, the governor told reporters: “I can’t move this election or change it on my own. My hands are tied.” And he acknowledged Monday that a Republican court challenge is “likely.”

“I just absolutely believe the people of Wisconsin are ready for this and will embrace it, and I’m counting on the judicial system to feel the same,” Evers said. “Regardless of the legal issues, I absolutely have the belief that the governor has to step up and stand up for those people. No one else is.”

Evers also argued in a court filing Monday that he does have the authority to act in an emergency such as the pandemic.

Legal experts were divided on the subject. Michael Morley, a law professor at Florida State University, tweeted that Evers’s action “appears to exceed his power under Wisconsin law” because the state lacks an emergency statute specifically governing the electoral process.

Republicans had opposed moving the election date with legislation, arguing that doing it so late in the process would sow confusion and create a leadership vacuum in cities and towns holding contests for municipal posts that will be vacant as early as mid-April.

Evers’s order Monday both postponed Tuesday’s voting and extended the terms of thousands of municipal officials whose terms expire in April and are on the spring ballot.

In his order, Evers said he was calling yet another special session on Tuesday, when he hopes lawmakers will pass legislation conforming state law with the new ballot deadline.

But Vos and Senate Republican leader Scott L. Fitzgerald had argued in their legal filing that the governor does not have authority to alter statutes or set elections. The two praised the court’s ruling late Monday and they thanked the state’s clerks for the work lying ahead.

“The safety and health of our citizens have always been our highest concern; that’s why we advocated for everyone to vote absentee,” they wrote. “Wisconsin has responded in droves. Over a million ballots have been requested for tomorrow’s election. We continue to believe that citizens should be able to exercise their right to vote at the polls on Election Day, should they choose to do so.”

“This election will proceed as planned,” they said.

Separately, the U.S. Supreme Court in its decision said lower courts had ordered an extension “which would allow voters to mail their ballots after election day, which is extraordinary relief and would fundamentally alter the nature of the election by allowing voting for six additional days after the election.”

The court’s liberals — Ruth Bader Ginsburg, Stephen G. Breyer, Sonia Sotomayor and Elena Kagan — objected.

“This Court now intervenes at the eleventh hour to prevent voters who have timely requested absentee ballots from casting their votes,” Ginsburg wrote.

She said it “boggles the mind” that the court majority was trying to apply the court’s usual rules in an unprecedented time of national turmoil.

“The question here is whether tens of thousands of Wisconsin citizens can vote safely in the midst of a pandemic,” Ginsburg wrote, adding: “Either they will have to brave the polls, endangering their own and others’ safety. Or they will lose their right to vote, through no fault of their own.”

Democrats and voting activists accused Republicans of trying to suppress voter turnout intentionally to help an incumbent candidate for the state Supreme Court, conservative Justice Daniel Kelly, keep his seat.

In late 2018, Republican lawmakers considered changing the date of the Democratic presidential primary, which was expected to draw high turnout, to protect Kelly’s candidacy. At the time, Fitzgerald said moving the Democratic contest to March would give the justice a “better chance” of winning.

Adding to the drama, Kelly also offered his own opinion on Twitter Monday before the court’s decision — even though he has been recusing himself from election-related cases. He did not participate in the decision, the court said later.

“From the very beginning of this campaign, all we have wanted is an election conducted according to the law,” Kelly wrote.While the Governor’s order is being challenged in court, we urge clerks, poll workers, and voters to stand ready to conduct the election tomorrow.”

He added in another tweet: “We can do two things at the same time: maintain the foundations of our democracy while taking reasonable precautions to keep people safe.”

President Trump offered his own boost to Kelly’s campaign Monday night, tweeting: “The Wisconsin Supreme Court ruled that tomorrow’s election will proceed as scheduled. VOTE for Justice Daniel Kelly tomorrow, and be safe!”

Local officials and civil rights advocates had commended Evers’s decision Monday — but with the caveat that the court could intervene.

“Governor Evers’ action today firmly places him on the right side of public health and the right side of history,” Milwaukee Mayor Tom Barrett said in a statement. “Wisconsin citizens can be proud that he is saving lives and bolstering our democracy.”

“We encourage those voting absentee to make every effort to return their absentee ballots by tomorrow to guarantee their vote is counted,” said Chris Ott, who heads the ACLU of Wisconsin. “We also ask those planning to vote in-person to check media reports on Tuesday, to confirm whether or not the Governor’s order to postpone still stands.”

Ott added that the “chaos and confusion” surrounding Tuesday’s election is “unacceptable” and underscores the need for coordinated preparations for the November elections.

Despite mounting concerns in recent weeks among voters and poll workers about the risk of Tuesday’s in-person voting, Evers waited until Friday to first call for the presidential primaries and local elections to be postponed.

He said he did not act earlier because he believed in-person voting could be safe because so many Wisconsinites voted by mail and because those planning to vote on Election Day would be widely dispersed among thousands of polling places across the state.

That is no longer true, with mass cancellations among poll workers forcing local election administrators to shutter hundreds of voting sites, the governor said. Milwaukee, for instance, announced late last week that it planned to open only five voting sites compared with the usual 180.

“Frankly, I don’t know how five polling places in the city of Milwaukee can be safe, and that’s why I’m doing what I’m doing,” Evers said at a news conference Monday.

Following Evers’s order, Green Bay Mayor Eric Genrich issued an order postponing voting until June 9.

But around the same time, the Wisconsin Election Commission issued guidance to local clerks, urging them to continue preparing for Tuesday.

“I know too much has already been asked of you, but we ask you to proceed with your Election Day preparations as we do not know the outcome of any possible litigation, and we need to be prepared if the election is held tomorrow,” wrote Meagan Wolfe, the state election administrator.

On Sunday, two Democratic appointees on the Wisconsin Elections Commission denounced the legislature for moving forward with in-person voting, warning that the move would put the lives of Wisconsin voters at risk.

“Your failure to address these profound issues and the safety of all of Wisconsin’s residents during yesterday’s special session is unconscionable and is an abdication of your constitutional responsibilities as our leaders,” said Ann S. Jacobs and Mark L. Thomsen in a letter to Fitzgerald and Vos.

In addition, the mayors of 11 Wisconsin cities — including Milwaukee, Madison and Green Bay — urged state Health Services Secretary Andrea Palm in a letter to use her emergency powers to postpone voting on Tuesday.

Clarification: An earlier version of this story imprecisely described a lower court’s order regarding the deadline for absentee ballots. The court said they could be received by April 13, but it did not set a postmark deadline.

Simmons reported from Milwaukee. Robert Barnes in Washington contributed to this report.