I did some calculations.
In Pennsylvania, 6,000,000 voted for a president in 2016.
This year they expect 3,000,000 mail in ballots and 68% of those mail in ballots have been requested by registered Democrats so far. That would make 2,040,000 Democrats voting by mail.
Let's say Biden has a 5 point lead and in the end wins it 52.5% to 47.5% if all votes are actually counted. That would be 3,150,000 total votes for Biden. Some guesses at #s:
2,040,000 Biden votes by mail (probably more when you factor in Independents)
1,110,000 Biden votes in person (probably less when you factor in Independents).
The in-person tally could be 1,110,000 Biden and 1,890,000 Trump. That's 63% Trump to 37% Biden on election night. And the Republicans who control PA will do everything they can to reject as many mail in ballots as possible.
Here's some more bad news:
Most Pennsylvania voters who participated in the June 2 primary did so by mail, which led to delayed results, the Philadelphia Inquirer reported.
An analysis by the Inquirer found that thousands of ballots were not counted because they arrived too late. Only 76 percent of ballots mailed in the three weeks before the election were counted, the paper found.
https://www.msn.com/en-us/news/politics/how-six-key-swing-states-handle-voting-by-mail/ar-BB18gbca
On the other hand:
If you requested a vote by mail ballot you can vote in person, but you can only vote once. During early voting or on Election Day, you can take your
mail-in ballot to a polling place, surrender it and receive a regular ballot.
https://www.abc10.com/article/news/verify/verify-can-you-vote-in-person-if-you-requested-a-mail-in-ballot/285-2ccdaa58-7013-4cad-a388-67cd7e40f23b
