Just how much of a lead do Democrats need in early voting to overcome a projected Republican turnout wave on Election Day? In battleground states, John Pudner writes at The Hill, they’ll need a 70/30 split, thanks to a number of factors. A lot depends on electorate modeling, but the split in voting intentions make it clear that the early-vote lead had better be substantial:

Forbes polling indicates that roughly half of all voters plan to vote early, with 62 percent of Democrats planning to vote early while 72 percent of Republicans plan to wait and vote on Election Day. If that happened and independents split evenly (last time Trump won them), then Democrats would need to win early voting at least 70 percent to 30 percent to be on pace to barely overcome a 31 percent to 69 percent disadvantage in partisan Election Day votes.

Let’s stipulate to this point up front:

It proves it in a sense: People can look at the same early voting returns and see wildly different things. https://t.co/etsz6Ur6dW

— Sean T at RCP (@SeanTrende) October 28, 2020

National numbers applied to state races creates problems, and party ID doesn’t always indicate the final vote. In battleground states, where both parties are relatively evenly positioned, the former issue may not be quite as much of a problem, but YMMV.

Anyway. This is where the Gallup party-ID polling becomes more useful. Its previous iteration suggested that Republicans had a slight advantage over Democrats (R+1) and near parity among independent leaners (D+3). In that shape, Pudner’s estimate might have been a little too soft on where Democrats need to end up. The latest data, released yesterday, shows a slightly better environment for Democrats, with a D+2/indie split D+8. That’s closer to the 2012 model of the electorate, one in which Barack Obama narrowly won re-election while Democrats only made marginal gains in the House and Senate.

We’ll get back to that in a moment, but let’s look at how Pudner’s test works in the four battleground states in which return data is available. Only one state, Pennsylvania, shows Democrats building the kind of early lead they need, with a 79/21 split — well ahead of the curve, actually. However, Democrats fall short in the other three:

In Iowa, Democrats have cast 336,780 early votes and Republicans cast 199,586, a 63 percent to 37 percent edge, which is well short of the 70 percent they need to hit. Advantage goes to Republicans in Iowa.

In Florida, much has been made of Democrats flipping the early voting edge this year by outvoting Republicans 1,926,055 to 1,463,281 so far. However, that 57 percent of the partisan share is well short of the 70 percent they need to beat expected Republican turnout. Democrats’ early voting across the state is actually falling well short of what they would need to win if they lose Election Day 31 percent to 69 percent. Again, the advantage goes to Republicans in Florida.

Nevada might be the most telling state, though hardest to calculate. So far, Democrats outvoted Republicans 170,689 to 122,735 for a 58 percent to 42 percent edge. At first glance, that would be well short of the 70 percent they need in other states. However, in Nevada they only need a 59 percent to 41 percent edge in early voting since only about 1 in 5 voters will wait until Election Day. Ballots were mailed to all voters, and even in 2016 more than 60 percent voted by mail in the state. Advantage Republicans in Nevada.

But wait, readers might ask, what about the Gallup indie split at D+8? Doesn’t that change the calculation? Keep a couple of points in mind about that national metric. It gets driven by wide disparities in coastal states where Democrats dominate, which is why anything better than a D+5 for Republicans in congressional-preference polling is usually a sign of good news. Democrats don’t usually do well unless that indie split hits double digits, as the modeling I provided for the last six elections shows.

The only exception was the aforementioned 2012 election, but that has a huge caveat, too. In 2012, Obama deployed a far superior ground game to essentially perform to the Gallup model and to drag fellow Democrats across the line. Which side has the ground-game superiority in this election? Which side has registered more voters? Those are also important context points, neither of which favors Democrats in this cycle.

And which group will be the most successful in effectively casting ballots? NBC News raises that point again today:

Sixty percent of voters — nearly 70 million people — are projected to vote by mail nationwide during the coronavirus pandemic. Those who study absentee rejection rates estimate that 1 percent to 2 percent of those votes — potentially more than 1 million — won’t count, which could make a difference in battleground states.

“The vote-by-mail ballot rejections are going to be the hanging chads of 2000,” said Daniel Smith, a professor of political science at the University of Florida.

The risk of ballot rejection varies by demographics and geography. The rate of rejection tends to be higher for Black, Hispanic, female and younger voters, as well as for people who don’t usually vote by mail.

Experts say it also tends to be higher in states that don’t normally have a lot of absentee ballots — a category that includes the battleground states of Georgia, Nevada, North Carolina, Pennsylvania and Wisconsin. All five had less than 10 percent of turnout by mail in 2016, and they will see huge increases in mail votes this fall.

The 1-2% range applies to normal absentee balloting. New mass-vote-by-mail systems have much higher failure rates, as we saw in primaries earlier this year. In California, estimates of ballot failure ran between 3-5%, as it did in New York, but in NYC it ran closer to twenty percent. If Democrats are mainly voting by mail in these battleground states and sustain a 3-5% failure rate, that may well be enough to decide the entire election — a point on which Donald Trump warned, although he foolishly highlighted fraud rather than incompetence.

Basically, this means that Pudner might have needed to push his threshold up as high as 75%. And it means that we should all gird our loins for plenty of outrage in the weeks ahead.