[U]ntil the [exclusionary rule] rests on a principled basis rather than an empirical proposition, [the rule] will remain in a state of unstable equilibrium. Mapp v. Ohio, which overruled the then twelve-year-old Wolf case and imposed the fourth amendment exclusionary rule (the Weeks doctrine) on the states as a matter of fourteenth amendment due process, seemed to mark the end of an era. Concurring in Mapp, Justice Douglas recalled that Wolf had evoked a storm of constitutional controversy which only today finds its end. \u27 But in the two decades since Justice Douglas made this observation, the storm of controversy has not only intensified-but engulfed the fourth amendment exclusionary rule itself. It is now clear that once a provision ...