Josh Marshall looks into the charges of voter fraud that come up with every election and concludes there’s not too much to it:

If I successfully register Mickey Mouse to vote, on election day, Mickey Mouse will still be a cartoon character who cannot go to the local voting station and vote. Logically speaking there’s very little way a few phony names on the voting rolls could be used to commit actual vote fraud. And much more importantly, numerous studies and investigations have shown no evidence of anything more than a handful of isolated cases of actual instances of vote fraud.

Again, there have been numerous investigations of this. Often by people with at least a mild political interest in finding wrongdoing. But they never find it.