My experience in the underbelly of Canadian politics says there probably was a little fraud. Overzealous party workers can and do manipulate things a little, like voting for a dead relative or crossing state lines to vote twice. But that amount is very small. Maybe 500 in state like Michigan. And if D and R workers are both doing it, these fraudulent votes are cancelling each other to some degree.
If there were massive fraud, organized by high-level campaign managers to move 10,000s of votes, the election authorities would have likely heard about it weeks before the election. Certainly within a few days after the election--and there would have been a lot of evidence.
The Trump campaign team is using a well known fact and making it much bigger than it really is. And too many people are buying into this message. Sad.
Time for a new way.