Obviously the US presidential election is not won by popular vote, but by votes in the electoral college. This means that, as in the 2016 election, the defeated candidate can obtain a larger total vote share.
With this in mind, what has been the lowest percentage of the vote that a President has been elected on?
A related question: What is the lowest possible share of the vote that a candidate could win the Presidency with; assuming two candidates, with every voter choosing one or the other?
Two answers specific to that question are given here: What is the most someone can lose the popular vote by but still win the electoral college?