As you might expect, the source of the anxiety is different for each party. For the GOP, it’s a simple numbers game. A lot of mail-in ballots have come in already and it’s widely understood that Democrats are far more prone to vote by mail than Republicans are. The Quinnipiac poll of South Carolina that I wrote about earlier contained this eye-popping number in response to a question about whether voters there plan to vote in person or by mail:

If you’re a Republican and you’re hearing reports of an avalanche of mail ballots pouring in early, you’re left with a terrifying question. Is this simply evidence of a shift in preferences among Dems in how they vote? Or is this early evidence of massive turnout among Democrats this year?

Of the more than 9 million voters who requested mail ballots through Monday in Florida, Pennsylvania, North Carolina, Maine and Iowa, the five battleground states where such data is publicly available, 52 percent were Democrats. Twenty-eight percent were Republicans, and 20 percent were unaffiliated.

Additional internal Democratic and Republican Party data obtained by The Washington Post shows a similar trend in Ohio, Minnesota, New Hampshire and Wisconsin.

Even more alarming to some Republicans, Democrats are also returning their ballots at higher rates than GOP voters in two of those states where that information is available: Florida and North Carolina…

“It’s astronomical,” said one Republican strategist involved in Senate races who said he was “horrified” by the discrepancy and, like others interviewed for this report, spoke on the condition of anonymity to describe internal concerns. “You see these numbers in a state like North Carolina, and how can you not be concerned?”

Republicans could conceivably offset all of those votes by showing up in person on Election Day, but that’s where COVID becomes an X factor. If there are bad outbreaks in swing states on November 3, how many seniors and people with preexisting conditions who intended to vote for Trump will decide it’s too risky to go out and stay home? Mail-in votes were the party’s lifeline for those people. McConnell has reportedly spoken with Trump at least twice to try to get him to back off his crusade against voting by mail because of it, but to no avail. For Trump, in an odd way, I think it’s a matter of self-interest: He’d rather preserve his ability to claim that he was cheated if he loses by insisting that mail-in voting is hopelessly fraudulent than embrace mail-in voting and give himself every possible chance to win, knowing that he’s out of excuses if he doesn’t.

One political scientist who’s tracking this year’s voting by mail told WaPo that in some states upwards of 10 percent of turnout from 2016 has already been recorded — and it’s not even October. This guy thinks it’s possible that the number of votes cast this year *before* Election Day will exceed total turnout in 2016. We may have more votes on the books this fall before polls open on November 3 than we had when polls closed last time.

What do Democrats have to be anxious about, then? Read this post from last week if you missed it. Partly they’re worried about how Trump will exploit their mail-in advantage to his own ends. If he leads when polls close on Election Day because of the surge in Republican same-day voting, he’ll claim that he won and that the counting of Democratic mail-in votes afterward that ends up erasing his lead is a product of cheating. Voting in person, either on Election Day or through early voting, would deny him that talking point, which is why lefty organizers are suddenly pushing people to eschew mail ballots and go to the polls instead.

But the other reason they’re worried is that mail ballots really are less reliable than ballots cast in person. We saw a small-scale example of what can go wrong a few days ago in Pennsylvania. Imagine that happening to hundreds of thousands of votes for Biden in states where the race is tight and it may mean the difference between victory and defeat. From the Atlantic:

Mail votes require several steps, and different steps in different locations, including postmarking the ballots, signing in various places, and using the proper number of envelopes. For that reason, it can confuse first-time voters, and even experienced voters used to queuing at local high schools. Two studies of the 2018 midterm elections in Florida and Georgia found that young and minority voters are especially likely to have their mail ballots rejected. (Both those voting groups skew Democratic.)

With millions of people voting by mail for the first time this year, experts expect more errors—and more rejected ballots. In the 2020 primaries, more than 550,000 mail and absentee ballots were disqualified, a much higher number than four years ago. The problem is especially severe in some swing states. More than 23,000 mailed ballots were rejected in the presidential primaries in Wisconsin—more than Donald Trump’s margin of victory in that state in 2016. Deep-blue districts have had the same problem: New York City alone threw out more than 84,000 ballots this primary season…

Democrats’ big edge in early voting and mail votes might be a salutary achievement. But in a close election, the combination of innocent mistakes by voters, mass litigation in close states, and conspiracy theories about mail-in voting could create the mother of all electoral headaches.

The Atlantic notes a recent analysis by the Philadelphia Inquirer that found more than six percent of the votes cast in last year’s municipal election were “naked ballots.” In Pennsylvania someone who’s voting by mail is supposed to enclose their ballot in an unmarked inner “secrecy” envelope and then place that in an outer envelope that contains their identifying information. A naked ballot is one where the voter forgets the inner envelope and places the ballot directly in the outer one. Any such ballot cast this fall is illegal, per the state’s supreme court.

Imagine Biden winning Pennsylvania by three or four points and Trump emerging with a one-point victory that hands him the presidency because six percent of the ballots were tossed for being “naked.” The country would be ungovernable.

The silver lining in this dark cloud of uncertainty is that the scenarios in which swing states spend days after November 3 counting ballots are exaggerated. An op-ed published last week in the Wall Street Journal noted that many states — notably Florida — begin verifying and counting mail ballots before the polls close on Election Day, which means those votes should be tabulated by the wee hours of election night. We’ll have a sense of who won in those places before we go to bed. Even in states like Michigan where the count may take longer, the fact that mail ballots are trending heavily blue this year means we may have a good idea of who won even before those votes are tabulated. If, for instance, Trump and Biden are tied in MI after in-person voting, with only mail ballots remaining to be counted, it’s a very safe bet that Michigan has turned blue. Trump will still claim that he’s been cheated, of course, but Trump isn’t really the X factor in all this. Americans who might be inclined to believe him are. A same-day election result would help reassure them that everything was on the up-and-up.