The system is secure and robust, at least with regards to the mechanics of individual votings.
Among the main factors is its distributed nature. You just can't run a scam with senior citizen volunteers in thousands of individual precincts.
Then, there are observers. Famous case from this week's election was Republicans complaining that their two dozen(!) observers weren't allowed closer than 6 feet to the ballots.
If it were possible to manipulate the vote tabulation in any meaningful way, the GOP wouldn't need to go to all the lengths it does w.r.t. gerrymandering, purging voter roles, coming up with new requirements for voting, or closing voting precincts.
Among the main factors is its distributed nature. You just can't run a scam with senior citizen volunteers in thousands of individual precincts.
Then, there are observers. Famous case from this week's election was Republicans complaining that their two dozen(!) observers weren't allowed closer than 6 feet to the ballots.
It would be impossible for fraud to happen on any regular basis and not coming to light. So the incidence of 0.00002% (https://www.vox.com/policy-and-politics/2017/4/26/15424270/v...) is somewhat informative.
If it were possible to manipulate the vote tabulation in any meaningful way, the GOP wouldn't need to go to all the lengths it does w.r.t. gerrymandering, purging voter roles, coming up with new requirements for voting, or closing voting precincts.