Almost never. Look at the vote totals for elections in 1960, 1968, 1980, and 1992. The popular votes were either exceedingly close or split between three parties. I’d point especially to 1960 and 1968. JFK barely won, and it’s likely due to some sort of electoral fraud in Illinois and Texas. 1968’s election was quite close in the popular vote AND saw a significant showing from a third party.

See the resources available at The Miller Center at the University of Virginia. They’ve got pretty good data on each of these elections.