Don’t you dare do it, Mitt! When good compromises with evil, only evil can profit. Do NOT endorse the one who despises you.
You may have a point about McCain, but as a generalization, would personally support a racist (of any 'race') or a Muslim on topics were there is agreement, such as if a racist Muslim group has a pro-life viewpoint, would support them in that one area, while taking a reproachful attitude toward them in others.
Sometimes, making deals with enemies is necessary to further your goals. You use them--and they use you. Allies are not the same as friends; they're marriages of convenience, to be annulled after the objective is reached.