@nooneinparticular Said
YOU are talking about using entrance polls to target and predict races that could be swung by a few thousand votes. I'm saying that if that's your goal, then you need to find close races that fall outside of the statistical uncertainty of those polls.
And as it turns out, the data obtained at entrance polls of the 2016 election would have come too late to impact the actual election.
And if you are using the entrance polls from one election (say in 2016) to make a plan to impact another election (say 2018), your data might well be out dated and irrelevant.... I depends on what is going on in the world, country, state, voting district, etc...
As to 2016, we know that the pre-election polls (the polls throughout 2015) were wrong (at least most of them), so would not have helped anyone's planning.
What a political party can do (in the USA), once they win an election, is to modify the voting districts (gerrymandering) and thus give the winning party an advantage over the losing party in the next election. This is kind of underhanded, but perfectly legal.
etc...
However, the full on illegal rigging of an is not likely.
From a theoretical perspective, the thing to do would be to hack the voting machines and/or the counting system with some coding prior to election day, thus when the votes came in, the malware would use an algorithm to change just enough of the votes for a candidate or set of candidates to win across numerous voting districts...but not by too many votes in any one location as that would flag fraud. Then provide a misdirection in the form of duping some people to commit voter fraud on a small scale.
At this point this
sort of thing is the stuff of fiction, though (again) theoretically possible.
At this point in time, the most practical way to impact an election is the gerrymandering thing combined with the flooding of all forms of information media (from News stations to social media) with fabricated bull s***. The gerrymandering stages the probability of who will get the most votes, and the false information things adds to that... after all humans, especially Americans, are gullible morons who will believe complete nonsense.