Oh? Citation needed; let's have some reliable support for that claim. You do have reliable, recent support for the claim, right? You're not just referring to the completely filthy '68 Chicago election shenanigans, right?
While you're digging that up, take a look at
this real nice Republican tactic.
Election tampering (and denial of same) has been going on for as long as there have been elections. No party has a monopoly on it.