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With the election just a few weeks away, Democrats are increasingly afraid to mail in their ballots—for understandable reasons. Donald Trump’s handpicked postmaster general enacted a raft of policy changes that have slowed mail delivery. (Under intense pressure, Louis DeJoy, a major Republican donor, announced that he would pause more scheduled measures until after the election, but also said he would not reverse many of the changes he already made.) Trump himself has openly admitted to hampering the Postal Service’s ability to handle a surge in mail ballots. And GOP officials around the country have taken myriad actions to make it harder for people to vote from home, including by restricting the use of ballot drop boxes—a highly popular option in universal vote-by-mail states like Colorado, Oregon, and Utah.

These actions have sent a message to voters that the Postal Service will screw up their ability to vote by mail, either by not getting their ballots to them on time, delivering them to elections officials too late to be counted, or maybe even losing them altogether. Unfortunately for Democrats, this anxiety could become a catastrophic problem. There’s evidence to show that if Democratic voters are worried about the USPS and decline to vote by mail, they won’t necessarily march to the polling place instead. Many of them just won’t vote at all. Given that Trump won key states by minuscule margins in 2016, such a drop-off could secure his reelection.

That fact has not yet fully sunk in with many prominent Democrats, who have responded to Trump’s manipulation of the mail system by encouraging voters to embrace multiple voting options. “We’ve got to vote early, in person if we can,” Michelle Obama said in her convention speech. “We’ve got to request our mail-in ballots right now, tonight, and send them back immediately and follow up to make sure they’re received, and then make sure our friends and families do the same.” Other influential voices have been more alarmist. New York Times columnist Tom Friedman wrote that he would “damn well get to my neighborhood polling station” because was scared of Trump’s “deliberate sabotaging of the U.S. Postal Service.”

These fears are now showing up in polling. In July, Emerson Polling found that 61 percent of Florida Democrats planned to vote via absentee ballot. In August, after Trump and DeJoy’s USPS interference made headlines, Emerson found that the number shrank almost in half. Just 32 percent of Florida Democrats said they planned to vote by mail. (Fewer Florida Republicans also said they planned to vote from home—27 percent in July to 19 percent in August—but the decline was nowhere near as dramatic.)

That drop wouldn’t be so worrisome if the mail-skittish Democrats were sure to vote in person. The problem is, they’re not. There’s a huge class of voters who, despite telling pollsters that they’ll schlep to the voting booth, actually won’t. And the best evidence from studies suggests that vote by mail is the most effective way to increase voter turnout, especially among younger and lower-propensity voters who tend to pull the lever for Democrats.

In 2014, for instance, Colorado voters in the 18-to-24-years-old bracket turned out 12 percentage points higher than was forecast by a generally accurate turnout model; at the same time, 25-to-34-year-olds outperformed expectations by 7 points. (And that was in a midterm election that had the lowest voting rates for an American election cycle in 70 years.) More broadly, in 2018, every vote-at-home state had a turnout rate of at least 10 percentage points higher among eligible voters than the national average.

Losing these marginal voters could have dire consequences in crucial swing states—like Florida, where a new NBC/Marist Poll shows Trump and Biden essentially tied in a dead heat, and where presidential elections over the last 20 years have been decided by hanging chads and endless recounts. In Pennsylvania, Quinnipiac found a full 47 percent of Democrats plan to vote by mail, compared to 13 percent of Republicans and 29 percent of independents. That’s great for Democrats, but if even a small percentage of those mail-friendly voters get skittish, Biden could see his margin of victory in the pivotal state disappear. Clinton lost there by less than two percentage points four years ago.

In the early months of the coronavirus outbreak, before the USPS sabotage, the states and municipalities that shifted to mostly mail-in voting saw substantial surges in voter participation. In a special congressional election in Baltimore and the nearby suburbs last April, turnout increased 10 points from a February primary that was held the old-fashioned way. It also had a much higher turnout the last time a special election was held in the district 24 years ago. Back then, in 1996, only 8 percent of registered voters cast ballots.

The boosted turnout was consistent with other vote-at-home experiments nationwide. In 2016, for example, 21 of Utah’s 29 counties had switched over to the system. The rest were still relying on polling places. One hilltop community just outside of Salt Lake City, however, was split into two counties, one that used vote by mail (Salt Lake County) and one that didn’t (Utah County). Salt Lake had a turnout rate nearly 18 percentage points higher than Utah.

That’s because vote by mail does what no other election reform does anywhere near as well: It turns non-voters into voters. (Automatic voter registration and early voting certainly help, but they tend to make it easier for people who already plan to vote.)

That could make the difference in 2020. Hillary Clinton lost, in part, because of non-voters. According to the Pew Research Center, roughly 30 percent of eligible voting Americans didn’t cast ballots in 2016. Nearly half of those voters were non-white and nearly two-thirds were under the age of 50, precisely the demographics in which the effects of vote at home are most pronounced.

If Democrats want to avoid another 2016, they can’t be afraid of voting by mail, even in the face of unprecedented obstacles created by Republicans. Otherwise, they likely won’t convince their supporters to vote by other means. They may scare them out of voting, period.

Eric Cortellessa

Eric Cortellessa, a Washington Monthly contributing editor, is a staff writer for Time magazine.