Current polling shows that split tickets is back like never before, when there is little to no evidence to this in actual reality.
There is like, Susan Collins winning in 2020, and thats about it, every other presidential election, even midterms, shows partisanship growing, by quite a lot.
It would defy all trends and logic for Biden to be this incredibly despised figure, and it not have any negative effect on downballot.
Dems aren't holding senate seats in Ohio and Montana(probably not Arizona, or open seat in Michigan either), if Trump is crushing Biden in nearly every battleground state.
Biden is either severely underestimated, or downballot democrats will come crashing down with him.