Imagine this scenario: The government learns there might be a dirty bomb hidden in your town, so the police start driving around with Geiger counters, looking for houses that have more radioactivity than normal. (Assume this is practically feasible, though there may be various potential difficulties with it.) Enter the courts: "No, no, no," they say, "that's an unconstitutional search, because it is an effort to determine what's in people's homes without probable cause and a warrant."
"Insanity!" some might say; and I'm pretty sure that judges would not, in fact, find a constitutional violation in such a situation. But existing Fourth Amendment precedents suggest that such police searches would indeed be illegal. And this, I think, helps show that the war on terror requires some special rules that differ from those used in ordinary criminal investigations.
The law's logic is often counterintuitive, even when it's ultimately sound. Communists, Nazis, and Islamo-fascists, for instance, are currently entitled to the same First Amendment protection as Democrats and Republicans. It may seem odd to let people claim rights under the very Constitution that they are trying to subvert. But bitter experience has shown us that the power to punish such bad speakers often ends up being used to punish good ones, too. Likewise, it might seem reasonable to provide less Fourth Amendment protection when the government is investigating really serious crimes, like murder. Why not give the police carte blanche, for instance, to search murder scenes?
But the Supreme Court unanimously rejected such a rule in a 1978 case, Mincey v. Arizona; and even Justice William Rehnquist—no fan of broad readings of the Fourth Amendment—agreed on this point. First, more serious crimes may make the police even more zealous and may thus make it even more necessary to guard against police overreaching. And beyond that, the court was understandably reluctant to draw constitutional lines based on subjective estimates of "seriousness." As Justice Potter Stewart (hardly a doctrinaire liberal) wrote in Mincey:
[T]he public interest in the investigation of other serious crimes is comparable [to the interest in investigating murder]. If the warrantless search of a homicide scene is reasonable, why not the warrantless search of the scene of a rape, a robbery, or a burglary? No consideration relevant to the Fourth Amendment suggests any point of rational limitation of such a doctrine.
So is a police car driving a Geiger counter through my neighborhood unconstitutional? (John Elwood, writing in a legal journal in the summer of 2001, was, to my knowledge, the first to raise this question.) Here's some purely precedential logic about that:
1. Pointing infrared thermal imagers at a home (for instance, to find evidence of heat lamps used to cultivate marijuana) constitutes a "search" under the Fourth Amendment. That's what the court held—in an opinion by Justice Antonin Scalia!—in last year's Kyllo v. United States. The court found that the government's "obtaining by sense-enhancing technology any information regarding the interior of the home … constitutes a search." And such searches of homes are allowed only if the police get a warrant based on probable cause to think that this particular home contains evidence of a crime.
2. A Geiger counter is sense-enhancing technology that detects information regarding the interior of the home: whether there's an unusual amount of radiation (rather than heat) present in the home.
3. As I noted above, the Fourth Amendment generally applies equally to investigations of all serious crimes.
4. Therefore, based on the most analogous precedent, citywide sweeps using a Geiger counter to detect radiation coming from homes—sweeps not based on any individualized probable cause as to any particular house—are unconstitutional.
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.