Trump is going to wear his decision to make Vance his running mate like an albatross around his neck for two reasons. First, Vance’s pungent criticisms of him over the years will feature prominently in commercials and at the debates. Second, Trump will be saddled with Vance’s far right positions on issues such as abortion and “cat ladies” whether he agrees with them or not. Any attempt to distance himself from his partner will only make his judgment in selecting him look that much more questionable.
Trump didn’t have to choose someone with such a long paper trail. His decision not to go with a completely obsequious cipher is what overconfidence looks like.