Is there a way to do double votes? That is on a ballot voting for Trump, also vote for Clinton, Stein, or whoever? That would invalidate the Trump ballot, but not change the total numbers elsewhere.
Those ballots like they used in Florida with the dangling chads-I read that was a sneaky way that they used to cheat with those. Simply ran a rod through a stack voting for the candidate they wanted to win. This would put a double vote on the ballot, so it would get invalidated.
No quick way to spoil a Trump POTUS ballot. Would have to mark a line (to fill in the arrow pointing to the choice) that is read by the scanner.
Very time-consuming, and would have to be secure from any witnesses observing the fraudulent activity on the ballots.
What if the new line marked is not filled in like all of the others on that ballot?
Hard to do this at the level of votes needed and avoid getting caught.