What percentage of US Presidents were victorious because of some kind of cheating or vote manipulation?

It is safe to say that all presidential races have some level of cheating taking place. That is because many people are crooked. On a percentage basis, it is at least 5% of the population that will be willing to bend their standards, if standards exist for them, to gain something of value they want to see happen, and of course there are the 1% sociopaths who will do anything to anyone at any time if it suits them. This is not a high percentage of people who are willfully wanting to do something that will affect an entire nation, but the issue truly here is whether the cheating actually sways an election one way or another. That is a function of how close the race turns out to be—it is only when the margins are razor-thin, usually, that cheating can be a deciding factor. That has happened in the past and is just a fixture of life in the corrupted earth plane you inhabit. One might say that elections are a selection by voters of the candidate of their choice, barring interference from vote manipulations that might be done to negate some individuals’ choices, so that is a wildcard always present. What this speaks to is the need for greater rigor of methodology; whether it can ever be guaranteed to be error-free is an open question; it is theoretically possible, but again it is a question of political will.