When asked what kept him up at night, Ben Wikler, who is responsible for delivering a must-win state in November as chairman of the Wisconsin Democratic Party, used to answer, “unknown unknowns.” He no longer has to wonder what such a risk might look like.

Presidential campaigns, parties and state election officials are scrambling to heed health warnings while safeguarding the democratic process against a growing coronavirus epidemic whose scope is difficult to predict.

Their planning has included advising voters not to lick their mail-in ballots, relocating polling places away from senior living communities, and weighing whether to move forward with plans to bring tens of thousands of visitors from around the world to Milwaukee and Charlotte for the planned Democratic and Republican summer conventions, respectively.

Former vice president Joe Biden’s digital staff was envisioning options for virtual campaigning if sweeping changes were necessary. Sen. Bernie Sanders’s campaign already has an elaborate streaming operation, which it said it could tap in the event that campaigning is curtailed. Already, both campaigns have been providing hand sanitizer at events.

Over the weekend, the AFL-CIO, the nation’s largest federation of unions, canceled a presidential forum scheduled for Thursday in Orlando, where Biden and Sanders (I-Vt.), the leading contenders for the Democratic nomination, had been scheduled to appear. It was the first such cancellation to have been attributed to the coronavirus’s spread.

Asked about the wisdom of holding campaign events, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said it “really depends.”

“If you want to talk about large gatherings in a place where you have community spread, I think that’s a judgment call, and if someone decides they want to cancel it I wouldn’t publicly criticize them,” he said during a White House briefing Monday.

None of the presidential campaigns has made significant changes, even as all emphasize they will follow the recommendations of health experts. President Trump’s reelection campaign said it was “proceeding as normal,” denying that a “Women for Trump” bus tour had been postponed because of the coronavirus, pointing instead to a “scheduling conflict.”

Still, the virus, which caused stocks to nose-dive on Monday, suddenly brought every assumption about the unfolding of the 2020 race into question — even the viability of activities as core to campaigning as knocking on doors. It also intensified fears about election interference and disinformation, after social media became host to false claims about last-minute voting changes on Super Tuesday.

“It’s an item on the agenda of every meeting,” Wikler said. “Everyone involved in politics is deep in scenario planning.”

Most immediately, that meant protecting voters participating in contests Tuesday in six states, including Washington, the epicenter of the outbreak in the United States.

The state votes by mail, lessening concerns about transmission of the virus, apart from the potential issue of saliva on ballots or envelopes. Election officials, pressing voters to use a wet sponge or a cloth as a sealant, launched a public education campaign on social media with the slogan “Whether healthy or sick, please don’t lick!” State officials were also advising that voters deliver their ballots to election drop boxes in an effort to spare postal workers the health risk.

Speaking on a panel at the state capitol last month, the director of elections for Washington’s most populous county named the coronavirus as one of the obstacles that keeps her “up at night.”

“I think things like that — those things that we maybe don’t have in the contingency plans, like a virus,” King County Elections Director Julie Wise said at the event, which was hosted in part by the secretary of state’s office.

Wise called 2020 a “doozy of a year” for election administrators.

“We often don’t — or ever — cancel or delay an election, so we’re still conducting an election regardless of if there is flooding, regardless of if there is a pandemic, regardless of if there is an earthquake,” she said.

At least 45 states have laws that anticipate Election Day emergencies such as natural disasters, but these laws vary widely, according to the National Conference of State Legislatures. In eight states, including Florida, Texas and Virginia, the governor has the statutory power to delay or reschedule an election.

But in most states, officials closest to the ground have little guidance so far beyond what has been publicly released by the Centers for Disease Control and Prevention. Meanwhile, messaging from the Trump administration has veered between caution and the president’s early assertions that fears of the virus have been overblown.

In Michigan, which has been a hub of recent campaigning before Tuesday’s vote, a spokesman for the Wayne County Health Department pointed to CDC recommendations in explaining how the county, which includes Detroit, was encouraging voters to protect themselves ahead of Tuesday’s primary.

Campaigns, meanwhile, said they were relying on local health departments, while also following state and federal guidance.

“We’re a campaign that believes in science, and we will go with what the science tells us,” said Ari Rabin-Havt, a deputy campaign manager for Sanders. “If we can’t campaign one way, we’ll campaign another way.”

Biden, who has been holding shorter events and spending less time greeting supporters on the rope line, was committed to “complying with reasonable risk mitigations,” his campaign said in a statement. “At the same time, we will continue to run an aggressive, national campaign to win the Democratic nomination and defeat Donald Trump.”

While the Trump reelection campaign uncharacteristically has not advertised a public rally for this week or beyond, Trump has not appeared to alter his schedule of fundraising meet-and-greet events or his practice of greeting supporters who are invited to be on hand when he lands at airports.

Trump attended events with donors on Monday in Florida and greeted a line of supporters on the tarmac in Orlando.

“Reports that the White House has issued formal guidelines to staff instructing them to limit in-person interactions and meetings are completely false,” White House press secretary Stephanie Grisham said in a statement.

After this week’s voting, the Democratic contest turns to several states that will vote March 17, including Florida, whose voting population includes a substantial portion of retirees and senior citizens.

Already steps were being taken to protect them during voting. Numerous senior living centers that ordinarily serve as precinct locations had moved to relocate voting off their campuses, while others were still examining their options, according to Steve Bahmer, the president and chief executive of LeadingAge Florida, an association representing senior-living facilities.

“Seniors tend to vote, and obviously there’s a lot of interest in the 2020 election,” Bahmer said. “Voter disenfranchisement is a key concern, and steps are being taken in advance to make sure that doesn’t happen.”

The complications will only deepen when the presidential contest enters the summer months. Right now, the CDC has advised people at higher risk of infection to avoid crowds. If that advice were to become broader, or if the government were to impose the type of travel restrictions introduced in other counties, it could impede the parties’ abilities to hold their nominating conventions this summer.

Committees overseeing both conventions said they were pressing ahead with their plans while monitoring developments.

“We prioritize the health and safety of attendees and have the utmost confidence in the administration’s work and preparations,” said Blair Ellis, a spokeswoman for the Republican convention, scheduled for August in Charlotte.

Joe Solmonese, the chief executive of the Democratic convention, set for July in Milwaukee, said in a statement that every convention requires “developing a number of contingency plans to provide for a variety of scenarios.

“As we prepare to welcome Americans to Milwaukee this summer, the convention team will remain in constant communication with the local, state, and federal authorities responsible for protecting public health and security,” he said.

Alex Halderman, a computer scientist at the University of Michigan, said it would be difficult to replicate the social experience of the convention. The balloting process involved in selecting a nominee, however, could probably be transferred to an online system, he said, citing Google software as a possible alternative.

As for voting itself, Halderman said mail-in ballots offer an efficient alternative to in-person participation. But there are barriers, he cautioned, including states that don’t offer no-excuse absentee voting. He also pointed to concerns about coercion that arise when large numbers of people are mailing in ballots rather than completing them in the privacy of a voting booth.

Four states hold all elections entirely by mail, and at least 21 states allow certain elections to be conducted entirely by mail, depending on the circumstances, according to the National Conference of State Legislatures.

There is little precedent for the waging of a presidential race against the backdrop of an epidemic on this scale.

The Spanish flu of 1918 was active during that year’s midterm campaign and election season. Local news reports from the weeks before and after that election suggested that the virus did impact planning, with some officials ordering voters to wear masks or advising against congregating publicly to hear election results.

“The election of 1918 is the only truly momentous American election ever to take place in the midst of a major pandemic,” the late professor Alfred W. Crosby wrote in “America’s Forgotten Pandemic: The Influenza of 1918,” published by Cambridge University Press. “Spanish influenza certainly affected campaigning: it canceled political meetings; doused that American political perennial, the torchlight parade; and obliged politicians to abandon their plans for last-minute whirlwind speaking tours.”

Crosby cast doubt on whether the flu had depressed voter turnout, noting that while there was a “sharp drop” in votes compared with 1916, 1918 was a midterm election, when voter interest is typically lower.