Voter fraud is pretty rampant in Minnesota. You can buy a list of the people who are registered to vote, but didn't vote in the last election for $45. You then bus in inner city types and seniors with "assistants" to "help them vote" that are allowed to go inside polling booths with the fraudsters to fill out their ballots. It is also common for voters to see that someone has already signed in to vote for them, anecdotally the judges have just said sign next to someone else's name then, as it doesn't matter.
The MNGOPAC Gun Owners Political Action Committee and a few libertarian candidates has discussed these issues at length at various get togethers.