Undecided voters?

I can understand why someone could be undecided whether they would vote or not. They might think “Trump or I won’t vote,” or “Biden or I won’t vote.”

I can understand why someone might be undecided whether they would vote for one of the major candidates or just throw away their vote on a third-party candidate. (Which I have done.)

But I can’t understand how someone could be undecided between Trump and Biden.