The major concern surrounding voting machine or ballot tampering is usually at early voting locations, since there it is typical to leave the ballot boxes and/or voting machines unattended overnight. The state I'm a poll worker in does have reasonable additional precautionary measures, such as printing and retaining daily open and close reports from the digital tabulators to guard against overnight ballot stuffing, but this does present an opportunity to do something like tampering with the machine so that it incorrectly tabulates future ballots.

Not really an easy attack but still a possible one, and these machines have not established a strong reputation for protection against something like a firmware implant

This state uses and retains paper ballots, so it would be yet more difficult to design an attack that would withstand an audit of the paper ballots. But some states don't...

> Even with electronic voting machines it is rare to get enough privacy to hide attempting to tamper with the back of the machine like this article discusses.

An electronic voting machine could be tampered with well ahead of voting day. Verification hashes and the like are only aggregates that are open to trickery on the way to the humans checking them, the ground truth is impossible for a human to process. We cannot sense the state of a computer without its help. In contrast to this, the initial emptiness of a physical ballot box is very much in the realm of human senses, it's perfectly safe to leave them unattended until voting starts.