> How difficult is it to hack the electronic voting system the US uses for elections?
"The electronic voting system" doesn't exist. There are multiple types of machines, software, etc. throughout the US. Some of these have proven to have significant vulnerabilities. In addition, the local boards of elections likely have rollup systems which could be compromised as well. "Insider threats" are another possibility-- for example, throw out some portion of the ballots in a precinct that's strongly on one side or another. Voter- and registration fraud are some of the easiest hacks to perform.
> What hacking do you think took place during the election?
It's quite possible that some of each of these occurred somewhere during the election. They've detected some non-citizens who voted, for example.
The net effect of "hacking", and of innocent errors is likely insignificant, given the hard-working and careful volunteers who man the precincts at election time.
