This rigged election scenario has the media scurrying to find people to say voter impersonation rarely happens and that Trump is dangerously undermining confidence in the system. It's another way for the fact checkers to prove him wrong.
While for most of us an election is pretty perfunctory with no stuffing of boxes, there are a lot of problems that make people suspicious.
Registration requirements, election districts and polling place locations that move every year, lines around the block in some states, voting systems that are confusing, misprinted ballots, election workers who don't know what they are doing, Black Panthers outside polling places, and on and on...little things that make you think the fix is in or at least that mistakes can be made.
Ever hear a discussion of voting systems and the "acceptable" error rate ?
Most of the fix is the media but there are lots of people who think it's rigged, and mix in the oft misunderstood Electoral College and the belief is widespread.