Nobody will vote for Biden per se. Votes cast for him will be exclusively those who want him purely as an alternative to Trump.
Trump voters are voting against the corrupt establishment machine. Trump did a pretty good job of steering the country to peace and prosperity which some voters will like too. Although he has messed up some of the time, and he is a bit of a braggart etc. But the bottom line is, he is enemy numbers 1 through 10 to the corrupt establishment that Trump voters want cleaned up. Trump voters aren't going anywhere when he is on the ballot.
A third choice, unless somehow it seen as an enemy of the establishment by Trump voters (very unlikely) will either be ignored by all sides as a wasted vote, or if they get any steam will split those who are voting against Trump. They won't get any Trump voters.
They want Nikki’s voters and Democrats who only object to Biden on his age.
They can hear a sound they heard and saw before.....that they’re hearing from a distnce.....
https://www.youtube.com/watch?v=TEiTKloMgBg