Fortunately, there are pretty simple policies we can enact to prevent fraud and give faith in elections (both in America, as well as other countries). If you care, I'd perhaps start at https://www.verifiedvoting.org/
More effective would be to preselect a precise number of votes for a few machines in a swing state, with totals just 3-4 percentage points higher than what polling indicates for that precinct. Email a few journalists before the election: "I'm a engineer working to hack the election for Clinton, but I'm sickened by it and I want to blow the whistle... attached are encrypted tallies for the voting machines we compromised in precinct XXX. I know we have a team in YYY and I think in ZZZ, but I wasn't able to get data for those machines out. Decryption keys will follow Nov 15th."
If I were Russia, I would arrange something so one or two polling stations end up casting many fraudulent votes for Clinton, just to call the entire election into question and give more ammo to the Trump campaign. Even if those instances had no serious impact on the results, the uncertainty alone could definitely cause significant civil turmoil.
https://en.wikipedia.org/wiki/End-to-end_auditable_voting_sy...
I also found this slide deck from Ron Rivest interesting:
Auditability and Verifiability of Elections ACM-IEEE talk March 16, 2016
If stuxnet is possible, a voting machine should be a piece of cake.