system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do we know voter fraud does not occur in the U.S.? Is it possible that it occurs undetected? What evidence should voter fraud theoretically leave behind?

I've been wondering about this for a while and want to get a straight answer. One of the reasons people condemn voter ID laws in the U.S. is because they claim voter fraud is a non-existent problem. Apparently, we know that voter fraud does not happen, and I'm not sure how.

To me, it seems like voter fraud is the kind of crime that would leave behind no evidence if performed successfully. That's the whole point; nobody is supposed to know you voted illegally. 

Based on my understanding, there is no evidence for widespread cases of voter fraud, but do we apparently know that nobody gets away with it undetected?
gpt
I suppose that there is no way to "know" that people don't commit voter fraud undetected.  However, several organizations and government entities have looked into it, and have found that the rate of in-person voter fraud is ridiculously low.

Typically in-person fraud occurs when someone goes to the polls and says that they are someone else.  This is very rare.  The reason is simple, there is no benefit for the fraud committing party to do it.  Persons who want to commit fraud are typically politicians or those directly connected to them.  In-person fraud would be a slow and time-consuming process which would leave a lot of witnesses.