The Trump campaign has always been obsessed with expanding the electoral map even though it's practically impossible for him to do that. Remember Parscale's New Mexico fixation? MN is just the latest iteration of that delusion. With Biden investing here, unlike Hillary, the state is a comfortable Likely Dem.
Also, just a random conspiratorial thought, would it really be that shocking for Republicans to try and gaslight everyone into thinking that a Clinton state is competitive in order to get Biden to divert funds towards it instead of a swing state? Fun thought, but who knows. Either way I'm glad Biden is advertising here, just to be safe.
I mean, Biden has more than enough $$ so i dont think thatll be an issue