But also if there are two votes for President it is a no vote. Easily enough to swing an election. Just add a vote for Hillary to a ballot for Trump = no vote.
Easy to cheat after person voted between the person’s vote at a precinct and wherever they go afterward, I guess. It does not seem possible to add or subtract once the votes are sealed. If vote boxes are tampered with in any way they do not get recounted so it would not be easy to add votes and expect to add to the original tally for a candidate.