Correct, it’s mostly Trump vs Not Trump. But the voters left over — even many “Not Trump” voters — are saying Biden is too old. Harris would inherit Biden’s voters and stand a chance at rallying the leftovers, given her ability to form cogent sentences and campaign/debate vigorously.
People keep saying he “barely won” like it’s true. He had the biggest margin of any election since 1996 except for Obama 2008! There aren’t going to be any Johnson/GHWB style blowouts in the foreseeable future.
Trump ended his presidency in disaster and Biden won thanks to a few tens of thousands of votes in three swing states. Yes, they added up electorally. But the margin in each was razor slim (same as when Trump won).
The point one, there’s no indication of Biden performing as well.