There is all sorts of voter fraud. I once overheard snowbirds saying they vote in their home state by absentee ballot and then vote where they are in the winter. There is little or no checking to see if people are registered in more than one location, even within a state.
Democrats fight any effort to require ID or otherwise clean up voting issues. That tells me all I need to know.
Yep,
Likewise college students can vote in the home district and at college, especially if it is in a different State.
Likewise people who move are still registered in their old location and can get registered in their new location. They are supposed to state on the registration form whether they were formerly registered in another location .... but there is no cross checking database of voter ID that I know of.