Riots on voting day, due to accusations of corruption. No good hacking the voting machines if the ballots never make it there in the first place ...
A fringe candidate catches the popular imagination, and late polls show that she/he could get enough of the vote to upset everyone's calculations. So the original plan of how to manipulate the results needs a last second change.
To head off plans exactly like what is happening, after being counted in Springfield, the paper ballots are going to another location for re-counting. That was amazingly kept secret, so there is a scramble of what to do now?
