Elections generally tilt one way or the other based on fractions of a percentage of the vote, in fact, a single vote can be the difference.

So, if two candidates are evenly matched, it’s possible that a whole state can go one way or the other based on just a few votes.

Note that this is not specific to the USA and I’m in Australia.

As far as “elections” go where there’s only one choice, that’s not an election but a dictatorship and from where I’m standing, the USA is heading in that direction at a breakneck speed.