This article was originally published at on July 30, 2020.

Trailing Joe Biden in polls, President Trump is attacking mail-in voting as a potential source of illegal Democratic votes on a near-daily basis. But the biggest risk of a pandemic-induced crush of mail-in votes isn't fraud, an extraordinarily rare occurrence in American elections. 

The real danger is a perfect catastrophe of administrative overload, postal delays and voter error that could lead to millions of absentee ballots not counting. And this year, unlike the past, those ballots are likely to be overwhelmingly Democratic.

Trump's denigration of mail-in voting, as well as differing attitudes about the seriousness of COVID-19, are poised to blow open an unprecedented partisan divide between votes cast by mail and those cast on Election Day. A July ABC/Washington Post poll found that a majority of Democrats (51 percent to 46 percent) plan to vote by mail this November, while nearly four in five Republicans (79 percent to 20 percent) still plan to vote in person.

A June 23 special congressional election in Upstate New York's 27th District offered a preview of this polarization: when in-person results were tallied on Election Night, Republican Chris Jacobs led Democrat Nate McMurray 69 percent to 29 percent. But three weeks later, with all but a handful of the district's more than 80,000 absentee ballots counted, Jacobs's lead dwindled to just 51 percent to 46 percent. 

So far in North Carolina, November absentee ballot requests by registered Democrats are up 702 percent over 2016 levels but up just 48 percent among Republicans, according to data compiled by Michael Bitzer, a political scientist at Catawba College. 

The problem for Democrats? Absentee ballots are rejected at higher rates than those cast in person. And academic studies have shown that younger voters and voters of color, some of Democrats' most reliable voters, are much more likely to cast mail ballots that are rejected and less likely to take steps to "cure" their ballots if election officials flag them for signature problems.

In 2016, according to an official report by the U.S. Election Assistance Commission, 318,728 of the nation's 33 million returned mail ballots were rejected, with the most common reasons being missing/non-matching signatures or the ballot being returned too late. An extensive study by Charles Stewart III, director of MIT's Election Data and Science Lab, estimates the true number of uncounted mail ballots in 2016 was a much higher 1.4 million - four percent of all mail ballots cast. 

"Voting by mail is twice as involved administratively than voting in person," explains Stewart. "If problems arise in mail voting, it's twice as hard to correct them than it is in person. And first time voters are more likely to have their ballots rejected."

But so far in pandemic-era primaries, rejection rates have been even higher, as ill-equipped and understaffed election offices strain to meet surging demand for mail ballots from voters inexperienced with casting them. In Wisconsin, over 9,000 requested ballots were never mailed to voters and 23,000 absentees (more than two percent) were rejected. In Kentucky's second-largest county, eight percent of absentees were tossed out. And in parts of New York City, upwards of 20 percent of absentees have been flagged as invalid.

Typically, legal challenges over which absentee ballots should count only arise in a handful of extremely close races. In 2008, Democrat Al Franken famously won Minnesota's Senate race by a scant 312 votes out of 2.9 million cast after Democrats fought in court to count 1,350 absentees they believed had been wrongly rejected. 

But record-smashing mail voting, unprecedented partisan polarization of that vote and unusually high rejection rates could significantly alter states' election math and plunge 2020 into a deep legal quagmire. 

For a moment, imagine a swing state where 42 percent of ballots are cast by mail and Biden carries them 80 percent to 20 percent, while Trump carries all other ballots 70 percent to 30 percent. If every ballot were to count, Biden would win the state 51 percent to 49 percent. But if eight percent of absentees were ruled invalid for various reasons - and the invalidated votes were reflective of the overall absentee pool - Trump would prevail by two hundredths of one percent.

This scenario explains why both sides are pouring tens of millions of dollars into litigating states' mail-in ballot rules and procedures this year. 

Democratic election mega-lawyer Marc Elias, who represented Franken in the 2008 Minnesota recount, is quarterbacking Democrats' efforts to prevent mail-in votes from being rejected. Elias is actively engaged in lawsuits in 18 states on everything from witness requirements and signature matching protocol to drop-off boxes and postmark/return deadlines - all of which differ by state.

"The rejection rates we've seen in the primaries have almost uniformly been above historic ranges," says Elias, who pointed to Michigan, North Carolina, Pennsylvania and Wisconsin as particular litigation hot spots. "I take Republicans at face value, that they don't want people to vote by mail."

In Pennsylvania, for example, Elias and Democrats have intervened against a Trump campaign lawsuit seeking to require counties to throw out absentee ballots that voters fail to enclose in the "secrecy envelope," an inner envelope meant to be tucked inside the larger return mailing envelope. In the June primary, 1.9 million Pennsylvania voters applied for absentee ballots, up from 107,000 in 2016; more than two thirds of those requests came from registered Democrats.

There's a relatively low risk of a meltdown in states accustomed to processing large quantities of mail ballots, such as Colorado, Oregon and Washington (where all elections have been conducted by mail for years) along with California, Florida and Arizona. But many of the highest-stakes Electoral College states face steep logistical curves as they rush to adapt to the COVID era: in 2018, mail-in votes were just six percent of all votes cast in Wisconsin and Georgia, four percent in Pennsylvania and three percent in North Carolina.

In Michigan, which adopted no-excuse absentee voting in 2018, ballots are mostly administered at the municipal level rather than the county level, which could multiply challenges and discrepancies. 

"I don't know how well each township clerk is set up to handle what's coming," notes GOP consultant Dan Hazelwood, who's working on races there. "Two voters who live a block away and apply for ballots at the same time could get their ballots weeks apart. It's a risk with an asterisk, and no one knows whether it's grave or minor."

Today, Biden's leads in battleground states are almost certainly robust enough to withstand a high mail-in rejection rate. But the presidential race could still tighten, and experts view widespread litigation over absentee ballots as inevitable because there are bound to be dozens of congressional races decided by close margins. 

In the past decade alone, seven Electoral College contests, 12 Senate races and 71 House races have been decided by less than two percentage points.

Growing fears over rejection rates could prompt Democrats to renew their focus on emphasizing in-person early voting as a means for those at lower health risk to relieve the burden on states' strained mail and Election Day infrastructure. But early in-person voting isn't available in some states, and there's no guarantee lines to vote early would be less crowded than voting on Election Day.

"If I were advising someone at lower health risk, I would say think about early in person voting," says Stewart of MIT. "But go early in the process and don't wait until the last minute."

To date, the conventional wisdom has held that Trump's assault on mail voting will backfire by depressing enthusiasm and turnout among GOP voters - and that could still turn out to be true. But it's also possible Trump, intentionally or not, is setting a trap by shifting more of his own vote to Election Day while Biden's ballots face a higher risk of rejection, legal limbo and lengthy counting delays. 

That should set off alarm bells for Democrats. After all, if Trump has thrived on anything in his political career, it's murkiness and chaos. 

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