Way too much detail to repost here but it all seems plausible and can be executed by a small number of operatives. The dems are routinely joked about as in the memes about dead people voting dem, but I have never seen the repub equivalent, do repubs regularly commit fraud like dems are alleged to? I also see dem fraud being caught and procecuted but rarely repub.
https://nypost.com/2020/08/29/political-insider-explains-voter-fraud-with-mail-in-ballots/
https://nypost.com/2020/08/29/political-insider-explains-voter-fraud-with-mail-in-ballots/