GOP Presidential Candidate Donald Trump raises the spectre of a stolen election, a rigged electoral system, a plot or plots to deny him (and the GOP) a rightful victory. This is not the first time Mr Trump has raised the spectre.
Here is the typology as outlined at Wikipedia. I am going to do some digging, to find the most recent and the most serious instances of electoral/voter fraud in the USA.
1.1.1Manipulation of demography