the mail in ballots never went away in fact it is even easier for those same voters to vote in 2024 than it is in 2020 because the hardest part (registering to vote) was done in 2020 assuming they have not moved they don't have change anything and a mail in ballot should show up in their mailbox without them doing anything at all this year so it really makes no sense why these voters are not showing up if the argument is "mail-in ballots"
United States