Is that really what happens? I would hope that if enough votes to come within a margin of error of changing the outcome were thrown out, the ballots would be re-cast. Or is there enough anonymity to make that impossible?
This is absolutely doable, and is really the logic behind most current physical election security procedures. Procedures are designed less to prevent tampering than to make tampering obvious. Re-voting can theoretically be done, because (public, real-time) records are kept of who voted at a particular polling place, not counting provisional ballots - look outside for a "street index" at your polling place.
(Source: am volunteering for the second time working the physical polls.)
I'd guess that repeating a vote favours whichever party has a particular demographic (younger?, less employed??) or whichever is better funded (to encourage/assist getting to polls) that subsequent votes get less and less attendees?
So, forcing a revote might be a way to swing a marginal seat in your favour.
They absolutely can be: see https://www.archives.gov/federal-register/electoral-college/..., specifically the section of the US code that speaks to "Failure to make choice on prescribed day" and "Determination of controversy as to appointment of electors". Basically - if for any reason a state can't pick electors on election day, it can do so afterwards by whatever (constitutional) method it desires; and if there's a disputed election and a state has a (pre-election) law enacted for deciding controversies that law just has to come to a decision within 6 days before the electors meet.
