<<Ahh, so no evidence other than "it's obvious.">>
Yeah, that's right, Ami. Sadly, McCain is not in the habit of making soul-baring confessions live on TV or leaving handwritten confessions of racism, prejudice and various other base motivations for his choices. How easy it would be if he were.
So, in the absence of direct evidence (no, nobody has caught him on camera, chaining blacks to the cellar walls of his eight houses and beating them unmercifully for minor infractions of his Servants' Code,) we have to rely only on informed speculation and circumstantial evidence, something nobody ever does in real life.