Great Fraud

To speak of fraud, irregularities or suspicions in the US presidential elections seems to be something as inadmissible as it is scandalous. It is one of the main democracies in the world, a country often used as an example of respect for institutions and consolidation of the representative democracy system. But are there maneuvers capable of twisting the outcome of an election? When margins are that tight, as was the case in some states, the answer appears to be yes. Which operations were held and