Plus, to really get to him, I bet the thing he most fears is something tarnishing his 'legacy'.
Even if there's no actual illegality in there, this could still 'ruin' his legacy. In many ways, it was the paranoia, crude language and racism in Nixon's tapes that did him in almost as much as the lawbreaking.
I've long thought that the only thing that could doom clinton with his rabid supporters is a candid tape of him uttering the "N" word with malice in his heart.
Then again, the FJB incident didn't seem to hurt hillary much, so who knows. The Kevlar Couple might just be impermeable.