The COVID-19 pandemic has already disrupted public life in a number of ways — large events are canceled, restaurants are closed and many of us are stuck at home — but a fundamental aspect of our democratic society could also be under threat: voting.

Already, eight states or territories have postponed their presidential primaries — but depending on how long this pandemic affects day-to-day life in the United States, it could impact the November general election, too. But this isn’t the first time our country has had to go to the polls in a time of crisis. Elections have occurred during economic catastrophes like the Great Depression as well as during both world wars. The good news is we’ve always managed to hold general elections — even in the midst of the Civil War — but the bad news is that our ability to vote is often hampered. And turnout has usually fallen because voting became harder or costlier in the face of natural or man-made calamities. Looking ahead to the November election, recent primary elections show that states need to be prepared for the worst when it comes to making sure people can vote despite a health crisis.

Take last Tuesday. Ohio postponed its election and in Illinois, where there isn’t a tradition of voting by mail, turnout was much lower than in the other two states that voted. (Florida and Arizona both generally cast a large percentage of ballots by mail.) There’s still a lot we don’t know about the current health crisis we find ourselves in — how long will the urgency of the coronavirus threat last, for example, or how things will look come November — but if we’re looking at elections comparable to our current moment, the most relevant may be the 1918 midterm.

That fall, in the waning days of World War I, the Spanish flu — a strain of influenza that got that name because Spain was one of the few countries to report on it freely — ravaged the United States, killing hundreds of thousands of people, many in the lead-up to the November election.

In response to this devastating disease, public health officials tried to limit its spread, but those mitigation policies affected political campaigns. Marian Moser Jones, a professor at the University of Maryland School of Public Health who studies the influenza pandemic, pointed to bans on public gatherings, which we’re seeing now too. “[Y]ou couldn’t have the usual election speeches, which were then even more important because you didn’t have television or radio,” Jones said. “[Candidates] had to actually campaign via newspaper editorials and mailings.”

This was particularly true out west, where the pandemic’s severity peaked in the days before the election. Even election night changed: There was a ban on the display of election returns on large boards outside of newspaper offices so that crowds wouldn’t gather to watch results come in, Jones told me. And in Los Angeles, “election officers locked themselves in each voting booth to count the votes and to prevent flu transmission.”

The Spanish flu also likely contributed to lower turnout on Election Day. About 40 percent of the voting-eligible population cast ballots in the 1918 midterm election, down sharply from the 50 to 52 percent that voted in the previous two midterms.

Jason Marisam, who studied the effect of influenza on the 1918 election as a legal fellow at Harvard Law School (he’s now an assistant attorney general in Minnesota), told me that it probably did have an effect on people voting. “The San Francisco Chronicle ran photos of Election Day, people lining up to vote all wearing these masks. They called it the first masked ballot in U.S. history,” said Marisam. “You have to think that that kind of mentality had an impact on turnout.”

Observers back in 1918 attributed the drop in turnout to the effects of the pandemic, too. “The Los Angeles Times estimated that the flu had kept 40,000 people away from the polls in San Francisco,” said Jones, adding that newspaper accounts of voting in Arizona and New Mexico talked about the disinfection of polling places and a “light vote” due to influenza and the absence of many men due to the war.

There’s one obvious complication when we examine turnout in 1918: the First World War. It’s difficult to separate out influenza’s effect on the election because around 2 million men were also fighting overseas in 1918, and not much was done to help them vote. That meant a sizable chunk of the electorate was effectively disenfranchised, as only men 21 years or older could vote in much of the country. (Remember, the 19th Amendment, which gave women the right to vote, wasn’t ratified until summer 1920.) Nonetheless, even if influenza only explains part of the drop-off in voter turnout, Marisam estimated it was still likely responsible for hundreds of thousands of people not voting.

But despite public health worries associated with influenza, Marisam told me he could find no evidence that people discussed postponing the 1918 election. Civic pride and patriotism were high during World War I, as war bond campaigns and propaganda from the Committee on Public Information encouraged Americans to do their part to support the war effort. And newspapers encouraged citizens to go to the polls despite the Spanish flu with headlines like “Every Loyal Californian Will Cast Vote At Election Today” in the Los Angeles Times. There also wasn’t a national debate over whether the results were legitimate, even though turnout was lower, and in some parts of the country, officials claimed influenza may have affected the results in congressional and local elections.

Of course, the 1918 election isn’t the only election to be held during a time of crisis (although it did take place during one of our country’s massive health crises). But just like the 1918 election, other federal elections also held during world wars saw depressed turnout.

In 1942, during World War II, the government tried to buoy turnout by passing the Soldiers Voting Act, which helped states send federal ballots to service members. It didn’t work particularly well: Less than 30,000 federal ballots were cast under its provisions and turnout in 1942 was very low — just 34 percent of the voting-eligible population cast a ballot, making it the second-lowest midterm turnout since the ratification of the 19th Amendment (only 1926, at 33 percent, was lower).

Trying to avoid the same problems in 1944, Congress passed a military ballot law ahead of the election that helped at least 2.6 million soldiers cast ballots — enough to make a difference for President Franklin Roosevelt in at least one state. (He won enough military votes in New Jersey to overcome his deficit among civilian votes, according to a contemporaneous study.) Still, turnout in 1944 was lower than the previous two presidential elections, and as you can see in the table below, voter turnout in elections during U.S. involvement in the two world wars was lower than in previous midterm and presidential elections.

Turnout fell during world wars compared to past elections Turnout among the voting-eligible population during WWI and WWII compared to the previous two midterm or presidential elections World War I Midterm Turnout 1910 52.0% 1914 50.4 1918 39.9 World War II Midterm Turnout 1934 44.5% 1938 46.6 1942 33.9 World War II Presidential Turnout 1936 61.0% 1940 62.4 1944 55.9 Source: U.S. Elections Project, Vital Statistics of American Politics

But it’s not just war and disease that have disrupted our elections. Sudden natural disasters have also impeded voting, as demonstrated by Hurricane Sandy, which hit the East Coast just days ahead of the 2012 election. New Jersey and New York were especially hard-hit, and leaders there had to work to ease voting access in the storm’s aftermath. In New Jersey, the government designated those displaced by the storm as “overseas voters,” which allowed them to email or fax absentee ballots, though some localities weren’t able to effectively handle the surge in absentee requests. And in parts of New York City, some voters had to cast ballots in tents because of the damage to polling locations.

It’s unlikely that Sandy’s effects altered the presidential outcome, given that both New Jersey and New York were safely Democratic, but turnout was down in areas affected by storm surge in New Jersey. One study from political scientists at Stony Brook University found that the storm possibly helped Barack Obama carry Virginia because of how it affected turnout in parts of the state.

Other disasters like 9/11 have disrupted our elections more dramatically. New York’s primary election was actually scheduled for Sept. 11, 2001, but the terrorist attack on the World Trade Center that morning prompted New York Gov. George Pataki to postpone the election, and the state instead held its primaries two weeks later. Obviously, this was an especially extreme case, but the suddenness of the delay is a reminder that sometimes elections can’t go on.

And it’s arguably why states should be preparing now for how voting will work in November. Turnout has usually declined in crisis elections — sometimes dramatically — and Illinois’s diminished turnout last Tuesday demonstrated that it could be challenging to hold an election if COVID-19 is still a significant danger come November, particularly if some states remain reliant on in-person voting.

Edward Foley, an election law expert at the Ohio State University’s Moritz College of Law, told me that states need to start adapting their voting systems. “The focus of attention should be on how to conduct a November election that maximizes opportunity for voter participation under current circumstances,” Foley said. “And that means ramping up capacity for vote by mail in states that are not traditionally used to vote by mail.”

However, many states could struggle to adopt vote-by-mail electoral systems because of legal, logistical and election security challenges. These include changing laws to provide more time for delivering, collecting and processing mailed-in ballots, as well as ensuring that a person only votes once. There are seemingly mundane obstacles to be overcome, like getting enough high-quality paper for printing ballots and having enough envelopes! It’s enough to make you wonder if there could even be talk of postponing the 2020 election.

But altering the presidential and congressional elections scheduled for November is very hard. It would require congressional action, and such a move would be unprecedented. Fortunately, state and federal governments have time to get ahead of many potential election challenges stemming from COVID-19. “If [states] start doing that preparation, I don’t anticipate any reason why Congress would want to change the date of the November election,” Foley said.

Whether our leaders will make the necessary changes, however, remains to be seen.