WASHINGTON -- The new coronavirus kept some voters and poll workers at home and hampered efforts to open some polling sites on Tuesday as three states held Democratic presidential primary contests amid a global pandemic.

Leaders in Ohio called off their primary just hours before polls were set to open as the federal government urged Americans not to gather in groups of 10 or more and asked older people to stay home. The state's Democratic Party said it was weighing options for challenging that move, which the Republican governor had pushed.

The move was so unprecedented that the chairman of the Democratic Party, Tom Perez, urged states to expand vote-by-mail, absentee balloting and polling station hours in an effort to keep the coronavirus from further disrupting the party's presidential nominating process. He also criticized Ohio for spreading confusion by cancelling voting just hours before it was supposed to begin on Tuesday.

It was the clearest indication yet that efforts to stop the spread of the virus could threaten to bring the primary to a near standstill in coming weeks, as many states push back their elections.

"The right to vote is the foundation of our democracy, and we must do everything we can to protect and expand that right instead of bringing our democratic process to a halt," Perez said in a statement.

Problems popped up across the country. In Illinois, an elections official and the governor traded blame over who was responsible for chaos at the polls there. In Okaloosa County in the Florida Panhandle, two dozen poll workers dropped out, leaving Elections Supervisor Paul Lux's staff scrambling to train replacements.

"We are at the honest end of the rope," Lux said.

The developments were a reminder of how the most elemental act of American democracy -- voting -- was being severely tested as Arizona, Florida and Illinois moved forward with primaries while confronting the impact of a global pandemic. The Democratic presidential primary between former Vice-President Joe Biden and Vermont Sen. Bernie Sanders is playing out as the virus' impact is becoming more tangible with schools closing across the country, workers staying home and restaurants and bars shuttering.

"It's definitely eerie," said Jesse Lehrich, a Democratic operative and former Hillary Clinton campaign spokesman who is based in Chicago.

The coronavirus, Lehrich said, seems to have cast a "shadow" over the Democratic primary race as debates over policy minutiae have taken a back seat to issues of life and death.

"Biden and Sanders are debating the merits of marginally different policies in this little pseudo-reality, while America is consumed by an unprecedented crisis," he said. "That's not a criticism of the candidates -- everything else in politics feels small in the shadow of coronavirus."

The big question Tuesday was the extent to which the coronavirus would affect turnout. Biden is moving closer to securing the Democratic presidential nomination but could face a setback if the older voters who tend to support him don't show up. Sanders, meanwhile, can't afford to lose support from young voters who have been his most loyal supporters.

Debra Cleaver, the founder of Vote.org, said she expected the coronavirus to make it even more difficult to get voters to the polls.

"People are prioritizing their day-to-day survival right now -- so they're not thinking of voting as a priority," she said.

Millions of voters have already participated in some form of early voting. But there were signs on Tuesday that voters -- and poll workers -- were staying home.

In Burbank, a small community southwest of Chicago, most of the voting stations stood empty at 8 a.m. Only 17 people had voted, a pace that officials said was unusually slow.

In Palm Beach County, Florida, 800 volunteer poll workers backed out Monday, and just 100 new volunteers offered to take their place.

Palm Beach County Elections Supervisor Wendy Sartori Link said three polling sites had to be moved and four opened significantly late because workers didn't show up and hadn't given notice, leaving her and her staff in a lurch.

"We probably should have been expecting it more than we were," she said.

In Illinois, there was a push to relocate about 50 Chicago-area polling places after locations cancelled at the last minute. Timna Axel, director of communications for the Chicago Lawyers' Committee for Civil Rights, said voters had been calling the group's hotline all morning to get help finding their polling places.

The steady flow of calls -- including from some polling place workers -- is "unusual for a primary," Axel said.

The chaos at the polls in Chicago led to fingerpointing between a city elections official and Illinois' Democratic governor after days of public debate over whether the state's primary should be postponed because of the coronavirus threat.

Jim Allen, a spokesman for the Chicago Board of Election Commissioners, said Tuesday that the board asked Gov. J.B. Pritzker last week to cancel in-person voting, but the governor refused. Pritzker said at a daily briefing on the coronavirus outbreak that state law doesn't give him the authority to make the sweeping changes that elections officials wanted.

"Let me tell you this: It is exactly in times like these when the constitutional boundaries of our democracy should be respected above all else. And if people want to criticize me for that, well, go ahead. I'll wear it like a badge of honour," he said.

Biden senior adviser Anita Dunn said Tuesday afternoon that the former vice-president's campaign watched early reports of low Chicago turnout with some concern, but those worries abated as voters cast ballots throughout the day.

"You hear there's no rush hour" at the polls, "and then you realize, well, there's no rush hour at all," because so many voters are working at home. That doesn't mean turnout won't be lower than it would have been, Dunn said, but that voting will be "more evenly distributed throughout the day."

Kate Bedingfield, Biden's deputy campaign manager, released a memo on turnout Tuesday afternoon predicting that "overall turnout will be roughly on pace for 2016 in Arizona and Florida and roughly on pace for 2018 in Illinois, and that voter turnout in all three states will reflect the population at large." Bedingfield cited strong early voting numbers in all three states.

The tumult surrounding the virus has left the primary campaign in a state of suspended animation.

Sanders, the last Democrat standing between Biden and the nomination, isn't planning to drop out, with his team seeing no downside to staying in the race as they assess how the coming days and weeks unfold.

Still, he faces an increasingly tough path to the nomination. About half of the delegates in the Democratic primary have already been awarded and, if Biden has another big night Tuesday, he will pad an already large and perhaps insurmountable lead. Sanders trails Biden by more than 150 delegates nationally, meaning he'd need to win more than 57% of those yet to be allocated to clinch the Democratic nomination.

But the coronavirus could amplify calls for Sanders to drop out of the race, especially if Biden comes out of Tuesday night's primaries in an even stronger position, Lehrich noted.

"It all feels like a bizarre formality given the moment -- a pointless subplot with a foregone conclusion, in the midst of an existential threat," he said.

The uncertainty surrounding the vote in many states comes as lawmakers on Capitol Hill negotiated with the Trump administration over a financial bailout package intended to contain the economic fallout from the virus. Speaking at a White House press briefing Tuesday, Trump insisted his administration was working fast to respond to the crisis, and he said eradicating the coronavirus would help ensure future primaries go on.

"We're getting rid of this virus. That's what we're doing," he said. "That's the best thing we can do."

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Associated Press writers Christina Cassidy and Bill Barrow in Atlanta, Katie Foody in Chicago, Kelli Kennedy and Terry Spencer in Fort Lauderdale, Fla., Don Babwin in Burbank, Ill., and Seth Borenstein in Washington contributed to this report.

Correction:

This story has been corrected to show that Louisiana moved its primary to June 20, not May