With widespread mail-in voting an abusive spouse could just fill in the ballot and drop it in the mailbox. No need to verify your spouse’s actions if you can just do it yourself.
In Russia all state employees, say school teachers, are told to vote the right way under no uncertain terms. But come the election day, and it is not physically possible to inspect what everyone is doing with paper ballots. If it was possible to digitally check voting, the regime would be even more repressive.
If you have an abusive spouse, voting is your last problem.
Just people who never bothered to update their voter registration.
Completed ballots are supposed to be verified by signature (at least in CA), but I have no idea how thorough this is.
And I imagine if they are mail in, could they even find people who completed all 4 ballots, then dropped them in some random mail box? From what I gather they just reject a vote if they can't match signatures.