I should add, as long as the sign-in table, ballot table personnel, and machine operators are all working for the same team--which is common in the all-Democrat neighborhoods where felons usually come from--it's easy to "check in" a voter, issue him a ballot, and then "cast his vote" without him being within 100 miles of the place.
Or at a higher level, simply to change the machine totals in the records, as long as another Democrat is available to sign off on the new total.
or just at home when the polls close and that person hasn’t voted yet. This has been going on for a long time in heavily Dem precincts where no Republicans volunteer to be election judges so Democrats happily step in for them