Change is trash, but this is quite interesting - Biden's margins grow a good amount when you add Klobuchar, or especially Harris into the mix as VP:
H2H:
Biden 49 - Trump 46
Biden/Whitmer 49 - Trump/Pence 47
Biden/Abrams 46 - Trump/Pence 48
Biden/Klobuchar 50 - Trump/Pence 45
Bden/Warren 47 - Trump/Pence 47
Biden/Harris 51 - Trump/Pence 43
Whitmer doing so poorly in her home state is surprising. It looks like she would not be a good VP pick. Harris doing so well is also surprising.
That said, I doubt the VP choice matters as much as this poll suggests it does.
