It is so ridiculously easy for a person to register in multiple locations and then request absentee ballots to vote multiple times. When you register to vote in one state nobody checks to see if you are registered in another state.
I could have voted 6 times in the last election, using the voter registration cards of my kids who live out of state and are registered elsewhere.
The only reason voter fraud is not completely out of control is because most people can't be bothered to vote even once, much less multiple times.
Many people simply change one letter in their name, and thus avoid detection.
In southwest border states, it was illegal in years past even to check to see if the voter in question was a legal citizen. (has that horrendous law been changed yet?)
That's how B1 Bob Dornan lost in ... 1998 or 2000, I forget.