I don’t see how the firmware, chips and software could possibly be contentiously audited to ensure that no one has introduced code to cheat.
It would not take that many lines of code to subtlety swing an election.
Tampering could be done at time of manufacture, during maintenance, transport, setup, updating. Or, in certain states, tampering would only need to be in a handful of precincts and that would swing statewide results.
Certainly cheating is also easy to do with paper ballots, or mechanical machines, but better, tighter human control of the voting and counting process could mitigate those cheating schemes, with electronic code, not so much.
True, but as I mentioned previously, it would take an army of dedicated techs working on each individual machine. Possible, yes; probable, no.