It will be difficult to stop all the fake ballots that will come from over-seas, already filled out.
They will arrive by the box-full via FedEx, UPS and DHL.
They will then be inserted into the ballot stream.
The protocol was once that in person ballots are primary results source. Next came the early votes, rolled-in.
Then the (legitimate) absentee ballots.
If needed to decide the election, the military ballots and ex-pat ballots were counted in.
Mail-in voting throws that aside and actually “nullifies” in-person balloting.
When the ends justify the means, the means become the ends.
All I know is I am sure that Trump and his team have plans to lot allow them to steal the election. I am not smart enough to figure out or speculate on how they will keep it clean.