This pretty well spells out the mysteries of voter fraud and how it is made to occur. Those illegals are certainly good for a lot of votes, unfortunately in polls already trending democrat so it really goes to artificially boosting the popular vote. California in particular.
The second group is dead voters and that take connivance at the local level and not terrible practical in smaller polls where folks know each other. Yet again a few hundred or even a few thousand voters are on the rolls and can be safely voted by an officer particularly if machines are available.
Then we come to outright machine manipulation. We do not know exactly how much bias can be spun but it does not need heavy manpower. Again though we are talking a modest shift in order to not disturb folks.
Yet we are talking about an easy three plus million votes here. They could not be used effectively where it actually mattered but did over represented some urban voting pools.
It was certainly enough to do in Mitt Romney in 2012