Q.E.D., as the logicians say. But surely this conclusion—that the government may not constitutionally conduct such searches—can't be right; and so it follows that one of the premises or the inferences must be wrong. The problem, I think, is that the court's precedents just cannot be taken this far. Sure, normally the Fourth Amendment applies equally to all serious crimes, and that's normally right. But finding dirty bombs must simply be different from fighting normal crime. Searches for weapons of mass destruction can't be treated like searches for marijuana-growing devices or even for murder weapons.
The Fourth Amendment, by its terms, only bans "unreasonable searches and seizures"—and it cannot be unreasonable to examine homes with Geiger counters in order to prevent a city from being rendered uninhabitable by an enemy bombing. Protecting people's privacy is important, and so is constraining government power. But sometimes we need extraordinary government power to protect against extraordinary threat.
Perhaps even house-to-house searches of a whole neighborhood might be constitutional, if there's reason to believe there's a dirty bomb hidden in the neighborhood, shielded with lead so Geiger counters won't find it—though in other circumstances such blanket searches would be quintessentially unconstitutional. But surely the Geiger-counter search, which is much less intrusive, is "reasonable" given the harm we need to avert. And this is true not becausethe court was wrong in Kyllo or Mincey or its other Fourth Amendment precedents dealing with ordinary crime. Rather, it's true because searches for weapons of mass destruction are just different. Yes, it's important to preserve constitutional rights even under dire circumstances. Yes, it's hard for the court to draw lines between different kinds of crimes. But some lines have to be drawn.
Of course, this opens the door to dangerous slippage. (The slippery slope, as I've written, is a serious concern in a legal and political system that's built on analogy and precedent.) Once this sort of search is allowed, well-intentioned people will naturally try to extend it to other actions that they feel are necessary. From searching for dirty bombs it's easy to draw an analogy to searching—again, without a warrant and probable clause—the homes and computers of some group that the police think might be involved in some plot to create such bombs. Even there we might be tempted to say, "All right, anything to save the lives of thousands, or more, of our countrymen." I'm certainly tempted to say that. But letting law enforcement decide who's possibly tangentially involved in a conspiracy, who might not be a conspirator but might have some evidence that might help unearth the conspiracy, and so on, would give law enforcement tremendous unsupervised power to search anyone they disliked.
Even honest officials may easily believe the worst of anyone who strikes them as potentially dangerous and credit tenuous claims of possible involvement in terrorist activity. And while most officials are honest, there are always some bad apples who would seize the opportunity to go after their political—or personal or departmental—enemies. What's more, as I wrote in Slate on Sept. 18, we're not in some temporary wartime situation where we can adopt emergency measures for a limited time. There'll always be terrorists and the risk of mass murder; we may never know for sure when that risk has greatly diminished. The measures we adopt today may thus be available to the government indefinitely. Imagine your least favorite president, from Nixon to Clinton, having powers like this in times of national turmoil. Police states can be built this way, and this isn't just hyperbole.
But while we should be constantly concerned about these risks, there are risks from erring in either direction: To repeat the obvious, not catching the terrorists is risky, too.
Moreover, insisting on identical Fourth Amendment rules for all threats may just mean less Fourth Amendment protection across the board, not more. I suspect that courts will find some way to allow searches for dirty bombs. If we distinguish these searches from normal law enforcement, then the tolerance for extra government power might be limited to these extraordinary cases. But if searches for radioactive material and searches for marijuana must be treated equally, then both kinds of searches will probably become equally permissible.