What if the odd and arch use of the word "purchase" gained purchase in Larry Tribe's brain because he'd watched "Raising Arizona." Suddenly "the idea of the image Tribe had of Kennedy's brain" is funny in a whole new way. "Justice Kennedy's brain/womb was a barren desert in which Breyer/Ginsburg's seed could find no purchase." Tribe thought Elena Kagan would be much better at.... what?
But it's not such an odd image. We speak of fertilizing minds and seminal ideas and gestating thoughts and mindfucks.