Prior to the midterms, Republicans were warning of an "epidemic of voter fraud" on the off chance that if the Democrats held the House, they would be able to claim that the victories were illegitimate. They won a historic victory, and so, as Ryan J. Reilly notes, all the groups claiming that Democrats were going to steal federal elections through fraudulent votes went mostly silent.
I say "mostly" because in some of the races where Republicans actually lost, the same tired conspiracy theories are being trotted out. As I pointed out last week, Michelle Malkin was whining about voter fraud in the Nevada Senate race because Latino voters, including those who didn't speak English, went heavily for Harry Reid (I wonder why?), but there are also congressional races in California and Missouri where Republican candidates lost by close margins and are blaming voter fraud despite a similar lack of evidence.
In the modern era, there's never been a proven case of someone stealing an election through the deliberate casting of fraudulent ballots, although in the conservative media, it's a given that it happens all the time. That's because conservatives think Democratic victories are inherently illegitimate, if not by the letter of the law, at least in the sense that liberals and Democrats aren't genuinely American. But the selective nature of voter-fraud claims is another hint at the self-conscious nature of this scam. Voter fraud only "occurs" when Republicans lose, and even then only as an explanation for why a Republican lost.